A223136 -id:A223136 - cp's OEIS frontend

A067803 Numbers n such that sigma(n)-sigma(n+1)=n.

Original entry on oeis.org

532, 954, 104944, 918080, 10368512, 25316030960, 35053995440, 45883878740

Offset: 1

Benoit Cloitre, Feb 07 2002

nonn

Mersenne primes are solutions to sigma(n+1)-sigma(n)=n. Conjecture: sequence gives even values only.

Subsequence of A223136. a(9) > 10^13. - Giovanni Resta, Jun 04 2016

Cf. A223136.

a(4)-a(8) from Donovan Johnson, Feb 01 2009

A227307 Numbers k that divide sigma(k) - sigma(k-1).

Original entry on oeis.org

2, 6, 15, 19, 207, 958, 1335, 1365, 1635, 2686, 2975, 3201, 4365, 4536, 8586, 14842, 16120, 18874, 19359, 20146, 24958, 33999, 36567, 42819, 53580, 56565, 64666, 74919, 79827, 79834, 84135, 92686, 109215, 111507, 116938, 122074, 138238, 147455, 161002, 162603, 166935

Offset: 1

Alex Ratushnyak, Jul 05 2013

nonn

Amiram Eldar, Table of n, a(n) for n = 1..1000

Cf. A000203, A053222, A223136, A223137, A227306.

A231546 is a subsequence.

With[{m = 200000}, 1 + Position[Differences[DivisorSigma[1, Range[m]]]/Range[2, m], ?IntegerQ] // Flatten] (* _Amiram Eldar, Dec 31 2024 *)

list(lim) = {my(s1 = 1, s2); for(k = 2, lim, s2 = sigma(k); if(!((s2-s1) % k), print1(k, ", ")); s1 = s2);} \\ Amiram Eldar, Dec 31 2024

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A067803 Numbers n such that sigma(n)-sigma(n+1)=n.

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A227307 Numbers k that divide sigma(k) - sigma(k-1).

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