OFFSET
1,3
COMMENTS
a(n) <= A024916(n-1) for n >= 2, with equality if and only if n is prime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Robert Israel, Plot of a(n)/n^2 for 1 <= n <= 20000
FORMULA
a(n) = Sum_{1<=k<=n; gcd(k,n)=1} A000203(k).
EXAMPLE
a(3) = sigma(1) + sigma(2) = 4.
MAPLE
f:= proc(n) local k; add(numtheory:-sigma(k), k=select(t -> igcd(t, n)=1, [$1..n])) end proc;
map(f, [$1..100]);
PROG
(PARI) a(n) = sum(k=1, n, if (gcd(n, k)==1, sigma(k))); \\ Michel Marcus, May 13 2019
CROSSREFS
KEYWORD
nonn,look
AUTHOR
J. M. Bergot and Robert Israel, May 12 2019
STATUS
approved