A225091 The odd part of the digit sum of 7^n.

1, 7, 13, 5, 7, 11, 7, 25, 31, 7, 43, 49, 37, 13, 29, 1, 13, 29, 73, 79, 19, 41, 97, 85, 73, 97, 7, 91, 133, 121, 59, 115, 103, 127, 71, 157, 17, 115, 65, 17, 71, 37, 17, 169, 175, 163, 187, 175, 17, 89, 23, 217, 49, 55, 217, 107, 211, 181, 241, 211, 199, 205

Offset: 0

Author

Vladimir Shevelev, Apr 27 2013

Keywords

• nonn
• base

Comments

Conjecture: the sequence contains all primes > 3.

Links

• Peter J. C. Moses, Table of n, a(n) for n = 0..1999

Crossrefs

Cf. A221858, A225017, A225039, A225040.

Programs

Maple

read(transforms) :
A225091 := proc(n)
    A000265(digsum(7^n)) ;
end proc: # R. J. Mathar, May 05 2013

Mathematica

Map[#/(2^IntegerExponent[#,2])&[Total[IntegerDigits[7^#]]]&, Range[0,99]] (* Peter J. C. Moses, Apr 27 2013 *)

PARI

a(n) = my(s = sumdigits(7^n)); s >> valuation(s, 2); \\ Michel Marcus, Dec 19 2018

Formula

a(n) = A000265(A066003(n)). - R. J. Mathar, May 05 2013