id:A143978 - OEIS Search Results

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Floor((2n(n+1)/3)).

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1, 4, 8, 13, 20, 28, 37, 48, 60, 73, 88, 104, 121, 140, 160, 181, 204, 228, 253, 280, 308, 337, 368, 400, 433, 468, 504, 541, 580, 620, 661, 704, 748, 793, 840, 888, 937, 988, 1040, 1093, 1148, 1204, 1261, 1320, 1380, 1441, 1504, 1568, 1633, 1700, 1768, 1837 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`Second diagonal of array A143979, which counts certain unit squares` `in a lattice. First diagonal: A030511.`
	FORMULA	`Floor(2n(n+1)/3).` `G.f.: x(1+x)^2/((1+x+x^2)(1-x)^3). a(n)= 2a(n-1) -a(n-2) +a(n-3) -2a(n-4) +a(n-5). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 05 2009]`
	CROSSREFS	`Cf. A143979.` `Sequence in context: A034856 A064609 A056738 this_sequence A071994 A023661 A157130` `Adjacent sequences: A143975 A143976 A143977 this_sequence A143979 A143980 A143981`
	KEYWORD	`nonn`
	AUTHOR	`Clark Kimberling (ck6(AT)evansville.edu), Sep 06 2008`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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