cp's OEIS Frontend

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

%I A225091 #22 Dec 19 2018 15:07:06
%S A225091 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,
%T A225091 97,7,91,133,121,59,115,103,127,71,157,17,115,65,17,71,37,17,169,175,
%U A225091 163,187,175,17,89,23,217,49,55,217,107,211,181,241,211,199,205
%N A225091 The odd part of the digit sum of 7^n.
%C A225091 Conjecture: the sequence contains all primes > 3.
%H A225091 Peter J. C. Moses, <a href="/A225091/b225091.txt">Table of n, a(n) for n = 0..1999</a>
%F A225091 a(n) = A000265(A066003(n)). - _R. J. Mathar_, May 05 2013
%p A225091 read(transforms) :
%p A225091 A225091 := proc(n)
%p A225091     A000265(digsum(7^n)) ;
%p A225091 end proc: # _R. J. Mathar_, May 05 2013
%t A225091 Map[#/(2^IntegerExponent[#,2])&[Total[IntegerDigits[7^#]]]&, Range[0,99]] (* _Peter J. C. Moses_, Apr 27 2013 *)
%o A225091 (PARI) a(n) = my(s = sumdigits(7^n)); s >> valuation(s, 2); \\ _Michel Marcus_, Dec 19 2018
%Y A225091 Cf. A221858, A225017, A225039, A225040.
%K A225091 nonn,base
%O A225091 0,2
%A A225091 _Vladimir Shevelev_, Apr 27 2013