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A174814
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a(n) = n*(n+1)*(5*n+1)/3.
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2
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0, 4, 22, 64, 140, 260, 434, 672, 984, 1380, 1870, 2464, 3172, 4004, 4970, 6080, 7344, 8772, 10374, 12160, 14140, 16324, 18722, 21344, 24200, 27300, 30654, 34272, 38164, 42340, 46810, 51584, 56672, 62084, 67830, 73920, 80364, 87172, 94354, 101920, 109880
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OFFSET
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0,2
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COMMENTS
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Also zero followed by bisection (even part) of A088003.
Numbers ending in 0, 2 or 4 (cf. 2*A053796(n)). Therefore we can easily see that a(m)^(2*k+1)==-1 (mod 5) only for m in A047219, while a(m)^(2*k)==-1 (mod 5) only for m in A016873 and k odd.
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LINKS
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FORMULA
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G.f.: 2*x*(2+3*x)/(1-x)^4.
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MATHEMATICA
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Table[1/3 n (1+n) (1+5 n), {n, 0, 50}] (* Harvey P. Dale, Feb 25 2011 *)
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PROG
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CROSSREFS
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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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