A078595 Number of pairs (x,y) 1<=x<=y<=n such that 1/x+1/y+1/n = 1/2.

0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 2, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

1,12

Comments

It seems that for n >= 43, a(n) = 0.

Links

Antti Karttunen, Table of n, a(n) for n = 1..11380

Prog

(PARI) a(n)=sum(i=1, n, sum(j=1, i, if(1/i+1/j+1/n-1/2, 0, 1)))

Crossrefs

Sequence in context: A291749 A370599 A253786 * A301989 A216513 A364419

Adjacent sequences: A078592 A078593 A078594 * A078596 A078597 A078598

Keyword

nonn

Author

Benoit Cloitre, Dec 08 2002

Status

approved