A120254 Number of independent nonempty subsets of integers in the interval [n^2+1, (n+1)^2-1] whose product is a square. Independence is over GF(2^m).

0, 0, 0, 0, 1, 0, 1, 2, 1, 2, 2, 2, 3, 2, 5, 3, 4, 4, 5, 4, 5, 7, 5, 6, 6, 7, 9, 5, 9, 7, 8, 11, 8, 11, 8, 10, 9, 13, 12, 10, 12, 12, 13, 14, 12, 15, 15, 12, 17, 14, 17, 14, 19, 15, 17, 18, 17, 17, 19, 20

Offset

1,8

Links

Table of n, a(n) for n=1..60.

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

Cf. A099500, A099501, A120253.

Sequence in context: A221531 A282970 A025807 * A263020 A068796 A154804

Adjacent sequences: A120251 A120252 A120253 * A120255 A120256 A120257

Keyword

nonn

Author

Martin Fuller, Jun 13 2006

Status

approved