Natural number
181 (one hundred [and] eighty-one ) is thenatural number following180 and preceding182 .
181 isprime , and apalindromic ,[ 1] strobogrammatic ,[ 2] dihedral number[ 3] decimal . 181 is aChen prime .[ 4]
181 is atwin prime with179 ,[ 5] five consecutive prime numbers:[ 6] 29 +31 +37 +41 +43 .
181 is the difference oftwo consecutivesquare numbers 912 – 902 ,[ 7] 2 + 102 .[ 8]
As acentered polygonal number [ 9]
181 is also a centered (hexagram )star number [ 11] Chinese checkers .
Specifically, 181 is the42 nd prime number[ 13] 16th full reptend prime decimal ,[ 14] reciprocal 1 181 {\displaystyle {\tfrac {1}{181}}} prime reciprocal magic square repeat180 digits with amagic sum M {\displaystyle M} 810 ; this value is one less than811 141 st prime number and49th full reptend prime (or equivalentlylong prime ) in decimal whose reciprocalrepeats 810 digits. While the first full non-normal prime reciprocal magic square is based on1 19 {\displaystyle {\tfrac {1}{19}}} 81 from a18 × 18 {\displaystyle 18\times 18} [ 15] 19 × 19 {\displaystyle 19\times 19} magic square has a magic constantM 19 = 19 × 181 {\displaystyle M_{19}=19\times 181} [ 16] 383 (alsopalindromic ).[ 17] [ a]
181 is anundulating number internary andnonary numeral systems , while indecimal it is the28th undulating prime [ 18]
^ Where the full reptend index of 181 is 16 = 42 , the such index of 811 is 49 = 72 . Note, also, that282 is 141 × 2. ^ Sloane, N. J. A. (ed.)."Sequence A002385 (Palindromic primes: prime numbers whose decimal expansion is a palindrome.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A007597 (Strobogrammatic primes.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A134996 (Dihedral calculator primes: p, p upside down, p in a mirror, p upside-down-and-in-a-mirror are all primes.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A109611 (Chen primes: primes p such that p + 2 is either a prime or a semiprime.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2016-05-26 .^ Sloane, N. J. A. (ed.)."Sequence A006512 (Greater of twin primes.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A034964 (Sums of five consecutive primes.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A024352 (Numbers which are the difference of two positive squares, c^2 - b^2 with 1 less than or equal to b less than c.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^a b Sloane, N. J. A. (ed.)."Sequence A001844 (Centered square numbers: a(n) equal to 2*n*(n+1)+1. Sums of two consecutive squares. Also, consider all Pythagorean triples (X, Y, Z is Y+1) ordered by increasing Z; then sequence gives Z values.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2016-05-26 .^a b Sloane, N. J. A. (ed.)."Centered polygonal numbers" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A005891 (Centered pentagonal numbers: (5n^2+5n+2)/2; crystal ball sequence for 3.3.3.4.4. planar net.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2016-05-26 .^a b Sloane, N. J. A. (ed.)."Sequence A003154 (Centered 12-gonal numbers. Also star numbers: 6*n*(n-1) + 1.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2016-05-26 .^ Sloane, N. J. A. (ed.)."Sequence A069131 (Centered 18-gonal numbers.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2016-05-26 .^ Sloane, N. J. A. (ed.)."Sequence A000040 (The prime numbers)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A001913 (Full reptend primes: primes with primitive root 10.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Andrews, William Symes (1917).Magic Squares and Cubes (PDF) . Chicago, IL:Open Court Publishing Company . pp. 176, 177.ISBN 9780486206585 MR 0114763 .OCLC 1136401 .Zbl 1003.05500 . {{cite book }}:ISBN / Date incompatibility (help ) ^ Sloane, N. J. A. (ed.)."Sequence A006003 (a(n) equal to n*(n^2 + 1)/2.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .^ Sloane, N. J. A. (ed.)."Sequence A072359 (Primes p such that the p-1 digits of the decimal expansion of k/p (for k equal to 1,2,3,...,p-1) fit into the k-th row of a magic square grid of order p-1.)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-09-04 .^ Sloane, N. J. A. (ed.)."Sequence A032758 (Undulating primes (digits alternate).)" .TheOn-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved2023-11-02 .
400 to 999
400s, 500s, and 600s 700s, 800s, and 900s
1000s and 10,000s
1000s 10,000s
100,000s to 10,000,000,000,000s
100,000 1,000,000 10,000,000 100,000,000 1,000,000,000 10,000,000,000 100,000,000,000 1,000,000,000,000 10,000,000,000,000
