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A005476
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a(n) = n*(5*n - 1)/2.
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25
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0, 2, 9, 21, 38, 60, 87, 119, 156, 198, 245, 297, 354, 416, 483, 555, 632, 714, 801, 893, 990, 1092, 1199, 1311, 1428, 1550, 1677, 1809, 1946, 2088, 2235, 2387, 2544, 2706, 2873, 3045, 3222, 3404, 3591
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: x*(2 + 3*x)/(1 - x)^3.
a(n) = A016754(n) - A133694(n+1). See Triangulated Diamonds illustration.
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MAPLE
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MATHEMATICA
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PROG
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(Magma) [Binomial(5*n, 2)/5: n in [0..40]]; // G. C. Greubel, Jul 30 2019
(Sage) [binomial(5*n, 2)/5 for n in (0..40)] # G. C. Greubel, Jul 30 2019
(GAP) List([0..40], n-> Binomial(5*n, 2)/5); # G. C. Greubel, Jul 30 2019
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CROSSREFS
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Cf. numbers of the form n*(n*k-k+4))/2 listed in A226488.
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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