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A022268
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a(n) = n*(11*n - 1)/2.
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14
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0, 5, 21, 48, 86, 135, 195, 266, 348, 441, 545, 660, 786, 923, 1071, 1230, 1400, 1581, 1773, 1976, 2190, 2415, 2651, 2898, 3156, 3425, 3705, 3996, 4298, 4611, 4935, 5270, 5616, 5973, 6341, 6720, 7110, 7511, 7923, 8346, 8780, 9225, 9681, 10148, 10626, 11115
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OFFSET
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0,2
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COMMENTS
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Number of sets with two elements that can be obtained by selecting distinct elements from two sets with 2n and 3n elements respectively and n common elements. - Polina S. Dolmatova (polinasport(AT)mail.ru), Jul 11 2003
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LINKS
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FORMULA
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a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 2.
a(n) = (1/9) * Sum_{i=n..10n-1} i. (End)
E.g.f.: (1/2)*(11*x^2 + 10*x)*exp(x). - G. C. Greubel, Jul 17 2017
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MAPLE
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MATHEMATICA
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PROG
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CROSSREFS
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Cf. index to sequence with numbers of the form n*(d*n+10-d)/2 in A140090.
Cf. similar sequences listed in A022288.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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