OFFSET
1,4
COMMENTS
It appears that, except for the first term, a(n)=n if and only if n is a prime congruent to 1 or 4 (mod 5).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
MAPLE
a:= n-> add(add(`if`(irem((i-j)*(i+j)-i*j, n)=0, 1, 0), j=1..i), i=1..n):
seq(a(n), n=1..100); # Alois P. Heinz, Oct 19 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
John W. Layman, Oct 19 2011
STATUS
approved