OFFSET
1,18
COMMENTS
Also number of divisors of 7*n-6 of form 7*k+5.
FORMULA
MATHEMATICA
a[n_] := DivisorSum[7*n - 6, 1 &, Mod[#, 7] == 3 &]; Array[a, 100] (* Amiram Eldar, Jun 25 2023 *)
PROG
(PARI) a(n) = sumdiv(7*n-6, d, d%7==3);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 25 2023
STATUS
approved