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129 (number)

From Wikipedia, the free encyclopedia
Natural number
← 128129 130 →
Cardinalone hundred twenty-nine
Ordinal129th
(one hundred twenty-ninth)
Factorization3 × 43
Divisors1, 3, 43, 129
Greek numeralΡΚΘ´
Roman numeralCXXIX,cxxix
Binary100000012
Ternary112103
Senary3336
Octal2018
DuodecimalA912
Hexadecimal8116

129 (one hundred [and] twenty-nine) is thenatural number following128 and preceding130.

In mathematics

[edit]

129 is the sum of the first tenprime numbers. It is the smallest number that can be expressed as a sum of three squares in four different ways:112+22+22{\displaystyle 11^{2}+2^{2}+2^{2}},102+52+22{\displaystyle 10^{2}+5^{2}+2^{2}},82+82+12{\displaystyle 8^{2}+8^{2}+1^{2}}, and82+72+42{\displaystyle 8^{2}+7^{2}+4^{2}}.

129 is the product of only two primes, 3 and 43, making 129 asemiprime. Since 3 and 43 are bothGaussian primes, this means that 129 is aBlum integer.[1]

129 is arepdigit in base 6 (333).

129 is ahappy number.[2]

129 is acentered octahedral number.[3]

References

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  1. ^"Sloane's A016105 : Blum integers".The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved2016-05-27.
  2. ^"Sloane's A007770 : Happy numbers".The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved2016-05-27.
  3. ^Sloane, N. J. A. (ed.)."Sequence A001845 (Centered octahedral numbers (crystal ball sequence for cubic lattice))".TheOn-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved2022-06-02.
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