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A083735
Pseudoprimes to bases 3 and 7.
3
703, 1105, 2465, 10585, 18721, 19345, 29341, 38503, 46657, 50881, 75361, 76627, 88831, 104653, 115921, 146611, 162401, 188191, 213265, 226801, 252601, 278545, 286903, 294409, 314821, 334153, 340561, 359341, 385003, 385201, 399001, 410041
OFFSET
1,1
FORMULA
a(n) = n-th positive integer k(>1) such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).
EXAMPLE
a(1)=703 since it is the first number such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).
MATHEMATICA
Select[Range[420000], !PrimeQ[#]&&PowerMod[3, #-1, #]==1&&PowerMod[7, #-1, #] == 1&] (* Harvey P. Dale, Mar 08 2014 *)
PROG
(PARI) is(n)=!isprime(n)&&Mod(7, n)^(n-1)==1&&Mod(3, n)^(n-1)==1 \\ Charles R Greathouse IV, Apr 12 2012
CROSSREFS
Intersection of A005935 and A005938. - R. J. Mathar, Apr 05 2011
Sequence in context: A035852 A214486 A045146 * A375918 A161021 A283521
KEYWORD
nonn
AUTHOR
Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003
STATUS
approved