A348689 a(n) = sigma(n) + sigma(n+1) - sigma(n+2), where sigma is the sum of divisors.

0, 0, 5, 1, 10, 5, 10, 10, 19, 2, 26, 18, 14, 17, 37, 10, 37, 17, 30, 38, 44, 0, 53, 49, 33, 26, 66, 14, 70, 41, 47, 57, 54, 11, 101, 69, 42, 26, 104, 36, 94, 56, 50, 90, 102, -4, 115, 88, 78, 67, 116, 32, 102, 72, 112, 110, 110, -18, 166, 134, 54, 73, 147, 67, 160, 86, 98, 78, 168, 21

Offset: 1

Author

Michel Marcus, Oct 29 2021

Keywords

• sign

Links

• Michel Marcus, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A104149, A348688.

Programs

Mathematica

Array[#+#2-#3&@@DivisorSigma[1,{#,#+1,#+2}]&,100] (* Giorgos Kalogeropoulos, Oct 29 2021 *)

PARI

a(n) = sigma(n)+sigma(n+1) - sigma(n+2);