A083733 Pseudoprimes to bases 2 and 7.

561, 1105, 2465, 3277, 8321, 10585, 18721, 29341, 46657, 62745, 75361, 104653, 115921, 162401, 219781, 226801, 252601, 278545, 294409, 314821, 334153, 340561, 399001, 410041, 449065, 488881, 512461, 530881, 534061, 552721, 574561, 587861

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..15498 (terms 1..138 from R. J. Mathar)

F. Richman, Primality testing with Fermat's little theorem

Index entries for sequences related to pseudoprimes

Formula

a(n) = n-th positive integer k(>1) such that 2^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

Example

a(1)=561 since it is the first positive integer k(>1) which satisfies 2^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

Prog

(PARI) is(n)=!isprime(n)&&Mod(2, n)^(n-1)==1&&Mod(7, n)^(n-1)==1 \\ Charles R Greathouse IV, Apr 12 2012

Crossrefs

Intersection of A005938 and A001567. - R. J. Mathar, Apr 05 2011

Sequence in context: A300629 A135720 A263403 * A339869 A375875 A214428

Adjacent sequences: A083730 A083731 A083732 * A083734 A083735 A083736

Keyword

nonn

Author

Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003

Status

approved