A341015 Numbers k such that A124446(k) = 1.

1, 2, 3, 4, 5, 6, 9, 18, 25, 27, 54, 81, 125, 162, 243, 486, 625, 729, 1458, 2187, 3125, 4374, 6561, 13122, 15625, 19683, 39366, 59049, 78125, 118098, 177147, 354294, 390625, 531441, 1062882, 1594323, 1953125, 3188646, 4782969, 9565938, 9765625, 14348907, 28697814

Offset

1,2

Comments

Numbers k such that A066840(k) and A124440(k) are coprime.

Contains all numbers of the forms 3^j, 2*3^j and 5^j.

Conjecture: the only term not of one of those forms is 4.

Links

Table of n, a(n) for n=1..43.

Formula

A124446(a(n)) = 1.

Example

18 is a term because A066840(18) = 13 and A124440(18) = 41 are coprime.

Maple

N:= 2*10^4: # 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 -> igcd(A66840[n], n*numtheory:-phi(n)/2)=1:
filter(1):= true:
select(filter, [$1..N]);

Crossrefs

Cf. A066840, A124440, A124446.

Sequence in context: A357570 A211676 A076299 * A136683 A200332 A303953

Adjacent sequences: A341012 A341013 A341014 * A341016 A341017 A341018

Keyword

nonn

Author

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

Extensions

More terms from Jinyuan Wang, Feb 07 2021

Status

approved