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A112415
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a(n) = C(1+n,1) * C(2+n,1) * C(4+n,2).
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2
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12, 60, 180, 420, 840, 1512, 2520, 3960, 5940, 8580, 12012, 16380, 21840, 28560, 36720, 46512, 58140, 71820, 87780, 106260, 127512, 151800, 179400, 210600, 245700, 285012, 328860, 377580, 431520, 491040, 556512, 628320, 706860, 792540, 885780, 987012, 1096680
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OFFSET
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0,1
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LINKS
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FORMULA
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O.g.f.: 12/(1-x)^5. (End)
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5); a(0)=12, a(1)=60, a(2)=180, a(3)=420, a(4)=840. - Harvey P. Dale, Jul 24 2011
Sum_{n>=0} 1/a(n) = 1/9.
Sum_{n>=0} (-1)^n/a(n) = 8*(3*log(2)-2)/9. (End)
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EXAMPLE
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n=0: C(1+0,1)*C(2+0,1)*C(4+0,2) = C(1,1)*C(2,1)*C(4,2) = 1*2*6 = 12;
n=10: C(1+10,1)*C(2+10,1)*C(4+10,2) = C(11,1)*C(12,1)*C(14,2) = 11*12*91 = 12012.
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MATHEMATICA
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Table[(n+1)(n+2)Binomial[4+n, 2], {n, 0, 30}] (* or *) LinearRecurrence[ {5, -10, 10, -5, 1}, {12, 60, 180, 420, 840}, 31] (* Harvey P. Dale, Jul 24 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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