A374970 - OEIS

A374970

Number of ordered primitive solutions (x,y,z,w) to x*y + y*z + z*w + w*x = n with x,y,z,w >= 1.

0, 0, 0, 1, 0, 4, 0, 6, 4, 8, 0, 22, 0, 12, 16, 22, 0, 36, 0, 42, 24, 20, 0, 76, 16, 24, 32, 62, 0, 104, 0, 66, 40, 32, 48, 146, 0, 36, 48, 140, 0, 152, 0, 102, 120, 44, 0, 220, 36, 120, 64, 122, 0, 196, 80, 204, 72, 56, 0, 380, 0, 60, 176, 178, 96, 248, 0, 162, 88, 280, 0, 444, 0, 72, 208, 182, 120, 296, 0, 396

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OFFSET

1,6

COMMENTS

a(n) = 0 if and only if n = 1 or n is prime. - Chai Wah Wu, Jul 26 2024

LINKS

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

PROG

(PARI) a(n) = sum(x=1, n, sum(y=1, n, sum(z=1, n, sum(w=1, n, (gcd([x, y, z, w])==1)*(x*y+y*z+z*w+w*x==n)))));

(Python)

from math import gcd

from sympy import divisors

def A374970(n): return sum(1 for d in divisors(n, generator=True) for x in range(1, d) for y in range(1, n//d) if gcd(x, y, d-x, n//d-y)==1) # Chai Wah Wu, Jul 26 2024

CROSSREFS

Cf. A066958, A374969.

Sequence in context: A340949 A021715 A327278 * A374969 A278210 A291540

Adjacent sequences: A374967 A374968 A374969 * A374971 A374972 A374973

KEYWORD

nonn

AUTHOR

Seiichi Manyama, Jul 26 2024

STATUS

approved