A341016 Numbers k such that A124440(k) is a multiple of A066840(k).

2, 3, 4, 6, 8, 10, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92, 96, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144, 148, 152, 156, 160, 164, 168, 172, 176, 180, 184, 188, 192, 196, 200, 204, 208, 212, 216, 220, 224, 228, 232, 236, 240, 244

Offset: 1

Author

J. M. Bergot and Robert Israel, Feb 02 2021

Keywords

• nonn

Comments

Numbers k such that k*A000010(k)/2 is a multiple of A066840(k).

Includes all multiples of 4.

Are 2, 3, 6 and 10 the only terms that are not multiples of 4?

Links

• Robert Israel, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A000010, A066840, A124440.

Programs

Maple

N:= 1000: # for terms <= N
G:= add(numtheory:-mobius(n)*n*x^(2*n)/((1-x^n)*(1-x^(2*n))^2),n=1..N/2):
S:= series(G,x,N+1):
A66840:= [seq(coeff(S,x,j),j=1..N)]:
filter:= n -> n*numtheory:-phi(n)/2 mod A66840[n] = 0:
select(filter, [$2..N]);