A361689 - OEIS

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A361689

The number of divisors of 2*n^2.

3

2, 4, 6, 6, 6, 12, 6, 8, 10, 12, 6, 18, 6, 12, 18, 10, 6, 20, 6, 18, 18, 12, 6, 24, 10, 12, 14, 18, 6, 36, 6, 12, 18, 12, 18, 30, 6, 12, 18, 24, 6, 36, 6, 18, 30, 12, 6, 30, 10, 20, 18, 18, 6, 28, 18, 24, 18, 12, 6, 54, 6, 12, 30, 14, 18, 36, 6, 18, 18, 36, 6, 40, 6, 12, 30, 18, 18, 36, 6, 30

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..80.

Project Euler, Problem 735. Divisors of 2n^2

FORMULA

a(n) = A000005(2*n^2) = 2*A078644(n).

a(n) = 2*A048691(n) if n odd, = 2*(1+A007814(n)) *A275367(n) if n even.

MAPLE

A361689 := proc(n)

numtheory[tau](2*n^2) ;

end proc:

seq(A361689(n), n=1..80) ;

PROG

(PARI) a(n) = numdiv(2*n^2); \\ Michel Marcus, Mar 21 2023

CROSSREFS

Cf. A000005, A078644, A048691, A007814, A275367.

Sequence in context: A174342 A111150 A166983 * A078611 A211376 A278249

Adjacent sequences: A361686 A361687 A361688 * A361690 A361691 A361692

KEYWORD

nonn,easy

AUTHOR

R. J. Mathar, Mar 20 2023

STATUS

approved