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A120254
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Number of independent non-empty subsets of integers in the interval [n^2+1, (n+1)^2-1] whose product is a square. Independence is over GF(2^m).
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3
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,8
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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.
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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)
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CROSSREFS
| Cf. A120253, A099500, A099501.
Sequence in context: A147657 A029232 A025807 * A068796 A154804 A053276
Adjacent sequences: A120251 A120252 A120253 * A120255 A120256 A120257
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KEYWORD
| nonn
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AUTHOR
| Martin Fuller (martin_n_fuller(AT)btinternet.com), Jun 13 2006
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