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Search: id:A062109
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| A062109 |
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Expansion of (1-x)^4/(1-2x)^4. |
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+0
2
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| 1, 4, 14, 44, 129, 360, 968, 2528, 6448, 16128, 39680, 96256, 230656, 546816, 1284096, 2990080, 6909952, 15859712, 36175872, 82051072, 185139200, 415760384, 929562624, 2069889024, 4591714304, 10150215680, 22364028928
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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If X_1,X_2,...,X_n are 2-blocks of a (2n+4)-set X then, for n>=1, a(n+1) is the number of (n+3)-subsets of X intersecting each X_i, (i=1,2,...,n). - Milan R. Janjic (agnus(AT)blic.net), Nov 23 2007
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LINKS
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Milan Janjic, Two Enumerative Functions
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FORMULA
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a(n) =(n+5)*(n^2+13n+18)*2^(n-5)/3 [with a(0)=1] =A055809(n-5)*2^(n-4) =2a(n-1)+A058396(n)-A058396(n-1) =sum{k<n}[a(n)]+A058396(n) =A062110(4, n)
G.f.:(1-x)^4/(1-2x)^4.
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PROGRAM
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(PARI) a(n)=if(n<1, n==0, (n+5)*(n^2+13*n+18)*2^n/96)
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CROSSREFS
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Sequence in context: A099063 A057223 A007466 this_sequence A118042 A006645 A094309
Adjacent sequences: A062106 A062107 A062108 this_sequence A062110 A062111 A062112
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KEYWORD
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nonn
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AUTHOR
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Henry Bottomley (se16(AT)btinternet.com), May 30 2001
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