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A102083 8*n^2+4*n+1. +0
4
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)
OFFSET

0,2

COMMENT

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

LINKS

Milan Janjic, Two Enumerative Functions

FORMULA

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]

EXAMPLE

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]

CROSSREFS

Cf. A085601.

Sequence in context: A043942 A004624 A045473 this_sequence A139866 A026918 A123972

Adjacent sequences: A102080 A102081 A102082 this_sequence A102084 A102085 A102086

KEYWORD

nonn,new

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com), Feb 14 2005

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Last modified November 25 08:46 EST 2009. Contains 167481 sequences.


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