A209187 - OEIS

A209187

Sum of divisors of n minus cototient of n.

1, 2, 3, 5, 5, 8, 7, 11, 10, 12, 11, 20, 13, 16, 17, 23, 17, 27, 19, 30, 23, 24, 23, 44, 26, 28, 31, 40, 29, 50, 31, 47, 35, 36, 37, 67, 37, 40, 41, 66, 41, 66, 43, 60, 57, 48, 47, 92, 50, 63, 53, 70, 53, 84, 57, 88, 59, 60, 59, 124, 61, 64, 77, 95, 67, 98, 67, 90, 71, 98, 71

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

PrimeFan, Listing of Esoteric Integer Sequences.

FORMULA

a(n) = A065387(n) - n. - Altug Alkan, Sep 30 2017

a(n) = A000203(n) - A051953(n). - Omar E. Pol, Sep 30 2017

Sum_{k=1..n} a(k) = c * n^2 / 2 + O(n*log(n)), where c = 6/Pi^2 + Pi^2/6 - 1 = 1.252861... . - Amiram Eldar, Dec 08 2023

MATHEMATICA

Table[(Plus @@ Divisors[n]) - (n - EulerPhi[n]), {n, 50}]