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A216822 Numbers n such that 2^n == 2 (mod n*(n+1)). 7
1, 5, 13, 29, 37, 61, 73, 157, 181, 193, 277, 313, 397, 421, 457, 541, 561, 613, 661, 673, 733, 757, 877, 997, 1093, 1153, 1201, 1213, 1237, 1289, 1321, 1381, 1453, 1621, 1657, 1753, 1873, 1905, 1933, 1993, 2017, 2137, 2341, 2473, 2557, 2593, 2797, 2857, 2917 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(17) = 561 is the first composite number in the sequence. - Charles R Greathouse IV, Sep 19 2012

Intersection of { A015919(n) } and { A192109(n)-1 }. - Max Alekseyev, Apr 22 2013

LINKS

V. Raman and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 2000 terms from V. Raman)

Mersenne Forum, Prime Conjecture

MATHEMATICA

Select[Range[1, 10000], Mod[2^# - 2, # (# + 1)] == 0 &] (* T. D. Noe, Sep 19 2012 *)

PROG

(PARI) is(n)=Mod(2, n*(n+1))^n==2; \\ Charles R Greathouse IV, Sep 19 2012

CROSSREFS

Cf. A069051 (prime n such that 2^n == 2 (mod n*(n-1))).

Cf. A217466 (prime terms of the sequence).

Cf. A217465 (composite terms of the sequence)

Sequence in context: A007521 A294919 A213050 * A217466 A078598 A155054

Adjacent sequences:  A216819 A216820 A216821 * A216823 A216824 A216825

KEYWORD

easy,nonn

AUTHOR

V. Raman, Sep 17 2012

EXTENSIONS

a(1)=1 prepended by Max Alekseyev, Dec 29 2017

STATUS

approved

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Last modified November 15 09:03 EST 2019. Contains 329144 sequences. (Running on oeis4.)