A066025 Numbers k such that gcd(sigma(k), sigma(k+1)) > k.

5, 12, 14, 70, 88, 125, 180, 204, 206, 220, 957, 1253, 1334, 1364, 1634, 1673, 1750, 1888, 1919, 2685, 2759, 2958, 2974, 3127, 4364, 5191, 7615, 8142, 8632, 9114, 11219, 12000, 12035, 14664, 14841, 18414, 18762, 18873, 19358, 20118, 20145, 20712, 24957, 25194

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Example

gcd(sigma(12), sigma(13)) = gcd(28, 14) = 14 > 12, so 12 is in the sequence.

Mathematica

Select[Range[1, 10^5], GCD[DivisorSigma[1, # ], DivisorSigma[ 1, # + 1]] > # &]

Prog

(PARI) { n=0; s=1; for (m=1, 10^9, t=s; s=sigma(m + 1); if (gcd(t, s) > m, write("b066025.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 07 2009

Crossrefs

Cf. A000010, A000203.

Sequence in context: A185871 A037007 A357999 * A009824 A286276 A314273

Adjacent sequences: A066022 A066023 A066024 * A066026 A066027 A066028

Keyword

nonn

Author

Joseph L. Pe, Dec 11 2001

Extensions

Definition and Example edited by Harry J. Smith, Nov 07 2009

Status

approved