A217465 Composite integers k such that 2^k == 2 (mod k*(k+1)).

561, 1905, 4033, 4681, 5461, 6601, 8481, 11305, 13741, 13981, 16705, 23377, 30121, 31417, 41041, 49141, 52633, 57421, 88357, 88561, 101101, 107185, 121465, 130561, 162193, 196021, 196093, 204001, 208465, 219781, 266305, 276013, 278545, 282133, 285541, 314821, 334153, 341497, 390937, 399001

Offset

1,1

Comments

Terms A019320(k) belongs to this sequence for k in A297415. - Max Alekseyev, Dec 29 2017

Links

Amiram Eldar, Table of n, a(n) for n = 1..12766 (terms below 10^12; terms 1..100 from Harvey P. Dale)

Mersenne Forum, Prime Conjecture, 2012.

Mathematica

Select[Range[400000], !PrimeQ[#]&&PowerMod[2, #, #(#+1)]==2&] (* Harvey P. Dale, Oct 12 2012 *)

Prog

(PARI) for(n=1, 10000, if((2^n)%(n*(n+1))==2&&isprime(n)==0, printf(n", ")))
(Python)
from sympy import isprime
A217465_list = [n for n in range(1, 10**6) if pow(2, n, n*(n+1)) == 2 and not isprime(n)] # Chai Wah Wu, Mar 25 2021

Crossrefs

Subsequence of A216822.

Contains A303531 as a subsequence.

Cf. A019320, A216822, A217466, A217468, A297415, A298758.

Sequence in context: A083732 A292367 A290805 * A097130 A110889 A205947

Adjacent sequences: A217462 A217463 A217464 * A217466 A217467 A217468

Keyword

nonn

Author

V. Raman, Oct 04 2012

Status

approved