OFFSET
1,17
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..1000
PROG
(PARI) m=80; v=vector(m); for(a=1, m, for(b=1, m, for(c=1, m, for(d=1, m, n=a+b+c+d; if(n<=m, if(b!=d&&a/b-c/d==(a-c)/(b-d), v[n]++)))))); v
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Oct 10 2018
STATUS
approved