cp's OEIS Frontend

A366799 Number of divisors d of n that are not of the form 4k+2, as permuted by the Doudna sequence.

%I A366799 #6 Oct 27 2023 16:38:55
%S A366799 1,1,2,2,2,2,3,3,2,2,4,4,3,3,4,4,2,2,4,4,4,4,6,6,3,3,6,6,4,4,5,5,2,2,
%T A366799 4,4,4,4,6,6,4,4,8,8,6,6,8,8,3,3,6,6,6,6,9,9,4,4,8,8,5,5,6,6,2,2,4,4,
%U A366799 4,4,6,6,4,4,8,8,6,6,8,8,4,4,8,8,8,8,12,12,6,6,12,12,8,8,10,10,3,3,6,6,6,6,9,9
%N A366799 Number of divisors d of n that are not of the form 4k+2, as permuted by the Doudna sequence.
%H A366799 Antti Karttunen, <a href="/A366799/b366799.txt">Table of n, a(n) for n = 0..16384</a>
%H A366799 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>
%F A366799 a(n) = A320111(A005940(1+n)).
%o A366799 (PARI)
%o A366799 A005940(n) = { my(p=2, t=1); n--; until(!n\=2, if((n%2), (t*=p), p=nextprime(p+1))); (t); };
%o A366799 A320111(n) = sumdiv(n,d,(2!=(d%4)));
%o A366799 A366799(n) = A320111(A005940(1+n));
%Y A366799 Cf. A005940, A320111, A366800 (rgs-transform).
%Y A366799 Cf. also A366797.
%K A366799 nonn
%O A366799 0,3
%A A366799 _Antti Karttunen_, Oct 27 2023