OFFSET
1,8
EXAMPLE
a(8) = 2 because 66*70*75*77*80 = 46200^2 and 65*72*75*78*80 = 46800^2 and the last square 65*66*70*72*77*78 = 360360^2 is formed by combining the first two and dropping doubled terms.
PROG
(PARI) A120254(n) = local(f, m, p); f=vecsort(vector(2*n, i, if(vecmax(factor(2*core(n^2+1+i-1), 2*n)[, 1])<=2*n, n^2+i, 0)), 0, 4); f=vecsort(vector(sum(i=1, #f, f[i]>1), i, f[i])); p=primes(primepi(2*n))~; m=matrix(#p, #f, i, j, core(f[j])%p[i]==0); matrank(matsolvemod(m, 2, 0, 1)[2]%2)
CROSSREFS
KEYWORD
nonn
AUTHOR
Martin Fuller, Jun 13 2006
STATUS
approved