OFFSET
1,1
EXAMPLE
a(1) = c(2,2) = (2 + 2 - 2) * (2 + 2 - 1) / 2 + 2 = 5 because gcd(2,2) = 2 > 1.
a(2) = c(2,4) = (2 + 4 - 2) * (2 + 4 - 1) / 2 + 2 = 12 because gcd(2,4) = 2 > 1.
PROG
(PARI) a(n)=if(n<1, 0, n=a(n-1); until(1<gcd(n-binomial(floor(1/2+sqrt(2 *n)), 2), binomial(floor(3/2+sqrt(2*n)), 2)-n+1), n++); n)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert A. Stump (bee_ess107(AT)msn.com), Oct 18 2002
STATUS
approved