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A376203
a(n) = A376202(2*n-1)/2.
5
0, 1, 0, 3, 0, 0, 6, 0, 0, 9, 6, 0, 0, 0, 0, 15, 0, 0, 18, 12, 0, 21, 0, 0, 21, 0, 0, 0, 18, 0, 30, 0, 0, 33, 0, 0, 36, 0, 0, 39, 0, 0, 0, 0, 0, 72, 30, 0, 48, 0, 0, 51, 0, 0, 54, 36, 0, 0, 0, 0, 0, 0, 0, 63, 42, 0, 108, 0, 0, 69
OFFSET
1,4
PROG
(Python)
from math import gcd
def A376203(n):
c, m = 0, (n<<1)-1
for x in range(1, m):
if gcd(x, m) == 1:
for y in range(x, m):
if gcd(y, m)==gcd(z:=x+y, m)==1 and not (w:=z**2-x*y)//gcd(w, x*y*z)%m:
c += 1
return c>>1 # Chai Wah Wu, Oct 06 2024
KEYWORD
nonn
AUTHOR
Tom Duff and N. J. A. Sloane, Oct 06 2024
STATUS
approved