A225017 Odd part of digit sum of 5^n divided by maximal possible power of 5.

1, 1, 7, 1, 13, 11, 19, 23, 1, 13, 1, 19, 7, 23, 17, 11, 29, 7, 1, 59, 61, 31, 67, 37, 41, 77, 79, 89, 17, 83, 91, 13, 53, 89, 103, 23, 109, 13, 31, 67, 13, 137, 29, 149, 151, 29, 7, 1, 29, 79, 151, 19, 13, 119, 127, 167, 49, 43, 211, 191, 199, 97, 187, 17, 83

Offset: 0

Author

Vladimir Shevelev, Apr 24 2013

Keywords

• nonn
• base

Comments

Does the sequence contain every prime greater than 5?

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..10000 (terms n = 0..999 from Peter J. C. Moses)

Crossrefs

Cf. A055566, A132740.

Programs

Maple

a:= proc(n) local m, r; m, r:= 0, 5^n;
      while r>0 do m:= m+irem(r, 10, 'r') od;
      while irem(m, 2, 'r')=0 do m:=r od;
      while irem(m, 5, 'r')=0 do m:=r od; m
    end:
seq(a(n), n=0..80);  # Alois P. Heinz, Apr 24 2013

Mathematica

Map[#/(2^IntegerExponent[#,2] 5^IntegerExponent[#,5])&[Total[ IntegerDigits[5^#]]]&,Range[0,99]] (* Peter J. C. Moses, Apr 24 2013 *)

PARI

a(n) = my(x = sumdigits(5^n)); x/5^valuation(x, 5) >> valuation(x, 2); \\ Michel Marcus, Dec 10 2018

Formula

a(n) = A132740(A055566(n)). - Michel Marcus, Dec 10 2018