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191 (number)

From Wikipedia, the free encyclopedia
Natural number
← 190191 192 →
Cardinalone hundred ninety-one
Ordinal191st
(one hundred ninety-first)
Factorizationprime
Prime43rd
Greek numeralΡϞΑ´
Roman numeralCXCI,cxci
Binary101111112
Ternary210023
Senary5156
Octal2778
Duodecimal13B12
HexadecimalBF16

191 (one hundred [and] ninety-one) is thenatural number following190 and preceding192.

In mathematics

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191 is aprime number, part of aprime quadruplet of fourprimes: 191,193,197, and199.[1] Because doubling and adding one produces another prime number (383), 191 is aSophie Germain prime.[2] It is the smallest prime that is not afull repetend prime inany base from 2 to 10; in fact, the smallest base for which 191 is a full period prime isbase 19.[3]

See also

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References

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  1. ^Sloane, N. J. A. (ed.)."Sequence A136162 (List of prime quadruplets {p, p+2, p+6, p+8})".TheOn-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  2. ^Sloane, N. J. A. (ed.)."Sequence A005384 (Sophie Germain primes p: 2p+1 is also prime)".TheOn-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  3. ^Wolfram MathWorld;Primitive Root
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