id:A137928 - OEIS Search Results

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The even principal diagonal of an 2nX2n spiral.

+0
4

2, 4, 10, 16, 26, 36, 50, 64, 82, 100, 122, 144, 170, 196, 226, 256, 290, 324, 362, 400, 442, 484, 530, 576, 626, 676, 730, 784, 842, 900, 962, 1024, 1090, 1156, 1226, 1296, 1370, 1444, 1522, 1600, 1682, 1764, 1850, 1936, 2026, 2116, 2210, 2304, 2402, 2500, 2602, 2704, 2810 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`2nX2n spirals of the form:` `(Example of n = 2)` `7...8...9...10` `6...1...2...11` `5...4...3...12` `16..15..14..13` `a(n) = A171218(n) - A171218(n-1). [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Dec 05 2009]`
	FORMULA	`a(n) = 2n + 4floor((n-1)^2/4) = 2n + 4A002620(n-1)`
	EXAMPLE	`a(1) = 2(1) + 4floor((1-1)/4) = 2` `a(2) = 2(2) + 4floor((2-1)/4) = 4`
	PROGRAM	`(Python) a = lambda n: 2n + 4floor((n-1)**2/4)`
	CROSSREFS	`Cf. A002061 (odd diagonal), A002620.` `Sequence in context: A039682 A111149 A123689 this_sequence A144834 A006584 A032246` `Adjacent sequences: A137925 A137926 A137927 this_sequence A137929 A137930 A137931`
	KEYWORD	`nonn,easy,new`
	AUTHOR	`William A. Tedeschi (fynmun(AT)hotmail.com), Feb 29 2008`

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Last modified December 8 08:31 EST 2009. Contains 170430 sequences.

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