OFFSET
1,3
EXAMPLE
a(57)=5 because (57*k+1)/(k^2+1) is an integer for k = 1,2,5,7,57.
PROG
(PARI) a(n) = sum(k=1, n, denominator((n*k+1)/(k^2+1)) == 1); \\ Michel Marcus, Feb 17 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Dec 29 2001
STATUS
approved