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Search: id:A102083
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| 1, 13, 41, 85, 145, 221, 313, 421, 545, 685, 841, 1013, 1201, 1405, 1625, 1861, 2113, 2381, 2665, 2965, 3281, 3613, 3961, 4325, 4705, 5101, 5513, 5941, 6385, 6845, 7321, 7813, 8321, 8845, 9385, 9941, 10513, 11101, 11705, 12325, 12961, 13613, 14281, 14965, 15665
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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If Y and Z are 2-blocks of a 2n-set X then, for n>=2, a(n-2) is the number of 4-subsets of X intersecting both Y and Z. - Milan R. Janjic (agnus(AT)blic.net), Nov 18 2007
Equals binomial transform of [1, 12, 16, 0, 0, 0,...]. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Jul 19 2008
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LINKS
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Milan Janjic, Two Enumerative Functions
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FORMULA
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G.f.: (1+10x+5x^2)/(1-x)^3 - Paul Barry (pbarry(AT)wit.ie), Jun 04 2005
a(n)=16*n+a(n-1)-20 (with a(1)=1) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 16 2009]
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EXAMPLE
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For n=2, a(2)=16*2+1-20=13; n=3, a(3)=16*3+13-20=41; n=4, a(4)=16*4+41-20=85 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 16 2009]
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CROSSREFS
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Cf. A085601.
Sequence in context: A043942 A004624 A045473 this_sequence A139866 A026918 A123972
Adjacent sequences: A102080 A102081 A102082 this_sequence A102084 A102085 A102086
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KEYWORD
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nonn,new
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Feb 14 2005
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