A211004 - OEIS

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A211004

Number of distinct regions in the set of partitions of n.

1, 2, 3, 5, 7, 9, 12, 15, 18, 22, 26, 30, 35, 40, 45, 51 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	COMMENTS	`The number of regions in the set of partitions of n equals the number of partitions of n. The sequence counts only the distinct regions. For the definition of "regions of the set of partitions of n" (or more simply "regions of n") see A206437.` `Is this the same as A001840 for all positive integers? If not, where is the first place these sequences differ?`
	LINKS	`Table of n, a(n) for n=1..16.` `Omar E. Pol, Illustration of initial terms` `Omar E. Pol, Illustration of the seven regions of 5`
	EXAMPLE	`For n = 6 the 11 regions of 6 are [1], [2,1], [3,1,1], [2], [4,2,1,1,1], [3], [5,2,1,1,1,1,1], [2], [4,2], [3], [6,3,2,2,1,1,1,1,1,1,1]. These number are the first A006128(6) terms of triangle A206437 in which the first A000041(6) rows are the 11 regions of 6. We can see that the 8th region is equal to the 4th region: [2] = [2]. Also the 10th region is equal to the 6th region: [3] = [3]. There are two repeated regions, therefore a(6) = A000041(6) - 2 = 11 - 2 = 9.`
	CROSSREFS	`Cf. A000041, A006128, A135010, A141285, A182244, A186114, A186412, A187219, A193870, A194446, A194447, A206437, A211009.` `Sequence in context: A184017 A024195 A071423 * A062781 A145919 A058937` `Adjacent sequences: A211001 A211002 A211003 * A211005 A211006 A211007`
	KEYWORD	`nonn,more`
	AUTHOR	`Omar E. Pol, Oct 22 2012`
	STATUS	`approved`

Last modified January 18 14:07 EST 2021. Contains 340254 sequences. (Running on oeis4.)