id:A033570 - OEIS Search Results

Search: id:A033570

Displaying 1-1 of 1 results found.

page 1

Pentagonal numbers with odd index: (2*n+1)*(3*n+1).

+0
7

1, 12, 35, 70, 117, 176, 247, 330, 425, 532, 651, 782, 925, 1080, 1247, 1426, 1617, 1820, 2035, 2262, 2501, 2752, 3015, 3290, 3577, 3876, 4187, 4510, 4845, 5192, 5551, 5922, 6305, 6700, 7107, 7526, 7957 (list; graph; listen)

	OFFSET	`0,2`
	COMMENT	`If Y is a 3-subset of an 2n-set X then, for n>=4, a(n-2) is the number of 4-subsets of X having at least two elements in common with Y. - Milan R. Janjic (agnus(AT)blic.net), Dec 16 2007`
	FORMULA	`G.f.: A(x) = (1+9x+2x^2)/(1-x)^3.`
	CROSSREFS	`Cf. A000326, A049452, A033568.` `Adjacent sequences: A033567 A033568 A033569 this_sequence A033571 A033572 A033573` `Sequence in context: A088596 A077293 A053682 this_sequence A163661 A142074 A102085`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com).`

page 1

Search completed in 0.002 seconds

Last modified November 8 07:45 EST 2009. Contains 166143 sequences.

AT&T Labs Research