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

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, 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, 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

Offset: 0

Author

Antti Karttunen, Oct 27 2023

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 0..16384
• Index entries for sequences related to binary expansion of n

Crossrefs

Cf. A005940, A320111, A366800 (rgs-transform).

Cf. also A366797.

Programs

PARI

A005940(n) = { my(p=2, t=1); n--; until(!n\=2, if((n%2), (t*=p), p=nextprime(p+1))); (t); };
A320111(n) = sumdiv(n,d,(2!=(d%4)));
A366799(n) = A320111(A005940(1+n));

Formula

a(n) = A320111(A005940(1+n)).