OFFSET
1,40
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..10000
FORMULA
For a prime p, a(p) = 1 if p has the final digit equal to 1, otherwise a(p) = 0.
a(n) = A330348(n) - 1. - Michel Marcus, Jul 19 2021
EXAMPLE
a(40) = 2 since there are 2 proper divisors of 40 ending with 0: 10 and 20.
MATHEMATICA
a[n_]:=Length[Drop[Select[Divisors[n], (Mod[#, 10]==Mod[n, 10]&)], -1]]; Array[a, 90]
PROG
(PARI) a(n) = my(x = n%10); sumdiv(n, d, if (d<n, d%10 == x)); \\ Michel Marcus, Jul 19 2021
(Python)
from sympy import divisors
def a(n): return sum(d%10 == n%10 for d in divisors(n)[:-1])
print([a(n) for n in range(1, 91)]) # Michael S. Branicky, Jul 31 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Stefano Spezia, Jul 15 2021
STATUS
approved