OFFSET
1,2
COMMENTS
For all k <= n, add n if k | n, otherwise add 1. For example, a(7) = 7 + 1 + 1 + 1 + 1 + 1 + 7 = 19.
FORMULA
a(n) = Sum_{k=1..n} n^c(n/k), where c(n) = 1 - ceiling(n) + floor(n).
a(p) = 3p - 2 for prime p.
MATHEMATICA
Table[n + (n - 1)*DivisorSigma[0, n], {n, 80}]
PROG
(PARI) a(n) = n + (n-1)*numdiv(n); \\ Michel Marcus, Jun 26 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Jun 25 2021
STATUS
approved