A168109 - OEIS

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A168109

a(n) = sum of natural numbers m such that n - 10 <= m <= n + 10.

55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 252, 273, 294, 315, 336, 357, 378, 399, 420, 441, 462, 483, 504, 525, 546, 567, 588, 609, 630, 651, 672, 693, 714, 735 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`0,1`
	COMMENTS	`Generalisation: If a(n,k) = sum of natural numbers m such that n - k <= m <= n + k (k >= 1) then a(n,k) = (k + n)(k + n + 1)/2 = A000217(k+n) for 0 <= n <= k, a(n,k) = a(n-1,k) +2k + 1 = ((k + n - 1)(k + n)/2) + 2k + 1 = A000217(k+n-1) +2k +1 for n >= k + 1 (see e.g. A008486). a(n) = (10 + n)*(11 + n)/2 = A000217(10+n) for 0 <= n <= 10, a(n) = a(n-1) + 21 for n >= 11.`
	LINKS	`Table of n, a(n) for n=0..35.`
	CROSSREFS	`Sequence in context: A043179 A043959 A004434 * A116055 A068898 A068899` `Adjacent sequences: A168106 A168107 A168108 * A168110 A168111 A168112`
	KEYWORD	`nonn`
	AUTHOR	`Jaroslav Krizek, Nov 18 2009`
	STATUS	`approved`

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Last modified May 21 19:04 EDT 2013. Contains 225504 sequences.