id:A088580 - OEIS Search Results

Search: id:A088580

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a(n) = 1 + sigma(n)

+0
2

2, 4, 5, 8, 7, 13, 9, 16, 14, 19, 13, 29, 15, 25, 25, 32, 19, 40, 21, 43, 33, 37, 25, 61, 32, 43, 41, 57, 31, 73, 33, 64, 49, 55, 49, 92, 39, 61, 57, 91, 43, 97, 45, 85, 79, 73, 49, 125, 58, 94, 73, 99, 55, 121, 73, 121, 81, 91, 61, 169, 63, 97, 105, 128, 85, 145, 69, 127, 97 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`Number of reflection subgroups of the (dihedral) Coxeter group of type I_2(n).`
	EXAMPLE	`a(2)=4. If W=<s, t\|s^2=t^2=1, st=ts> then the reflection subgroups are {1}, <s>, <t>, <s, t>.`
	CROSSREFS	`Cf. A000203.` `Sequence in context: A087711 A123128 A057064 this_sequence A036699 A036694 A085624` `Adjacent sequences: A088577 A088578 A088579 this_sequence A088581 A088582 A088583`
	KEYWORD	`easy,nonn`
	AUTHOR	`James East (jameseastseq(AT)hotmail.com), Nov 20 2003`

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Last modified July 26 23:19 EDT 2008. Contains 142293 sequences.

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