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A278337 Composite numbers n such that the sum of proper divisors of n divides 2^n+1. 0
15, 45, 99, 735, 1221, 1645, 1725, 1925, 2871, 4047, 8667, 13311, 16461, 19647, 21285, 27797, 39861, 52215, 52965, 65637, 67479, 74781, 106327, 124215, 126975, 155511, 181917, 240397, 244839, 257951, 315695, 344175, 412863, 442417, 445215, 449493, 707859, 1362079 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Are all terms odd? There are no even terms < 2*10^12.

LINKS

Table of n, a(n) for n=1..38.

MAPLE

select(n -> not isprime(n) and 2 &^n + 1 mod (numtheory:-sigma(n)-n) = 0, [$2..10^6]);

PROG

(PARI) is(n)=n>9 && !isprime(n) && Mod(2, sigma(n)-n)^n==-1 \\ Charles R Greathouse IV, Nov 18 2016

CROSSREFS

Cf. A000051, A001065, A278315.

Sequence in context: A060536 A014634 A303857 * A270563 A126228 A072251

Adjacent sequences:  A278334 A278335 A278336 * A278338 A278339 A278340

KEYWORD

nonn

AUTHOR

Robert Israel and Altug Alkan, Nov 18 2016

STATUS

approved

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Last modified March 31 02:36 EDT 2020. Contains 333135 sequences. (Running on oeis4.)