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Search: id:A131792
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| 1, 1, 2, 6, 21, 76, 280, 1045, 3936, 14925, 56892, 217791, 836706, 3224157, 12456225, 48232162, 187131664, 727309265, 2831193004, 11036424667, 43076087806, 168322335246, 658416150496, 2577945422410, 10102468839284, 39621592646545
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OFFSET
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0,3
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COMMENT
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Row n of triangle A131791 has 2^n terms for n>=0, where row sums and central terms of A131791 equals A028361: Product_{i=0..n-1} (2^i + 1).
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FORMULA
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a(n) = [x^n] Product_{j=0..n-1} [ (1 - x^(2^j+1) ) / (1-x) ] for n>0, with a(0)=1. - Max Alekseyev (maxale(AT)gmail.com), Aug 30 2007.
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PROGRAM
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(PARI) {a(n)=if(n==0, 1, polcoeff(prod(j=0, n-1, (1-x^(2^j+1))/(1-x)+x*O(x^n)), n))} - Max Alekseyev (maxale(AT)gmail.com), Aug 30 2007.
(PARI) {T(n, k)=if(n==0, 1, polcoeff(prod(j=0, n-1, (1-x^min(2^j+1, k+1))/(1-x)+x*O(x^k)), k))} - Martin Fuller (martin_n_fuller(AT)btinternet.com), Aug 31 2007
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CROSSREFS
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Sequence in context: A116798 A116821 A116772 this_sequence A144904 A151287 A101265
Adjacent sequences: A131789 A131790 A131791 this_sequence A131793 A131794 A131795
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Jul 15 2007
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EXTENSIONS
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More terms from Max Alekseyev (maxale(AT)gmail.com), Aug 30 2007.
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