id:A117621 - OEIS Search Results

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Number of double-perfect partitions of [1..n].

+0
2

0, 1, 1, 1, 1, 1, 3, 1, 3, 2, 3, 1, 7, 1, 3, 3, 6, 1, 8, 1, 7, 3, 3, 1, 17, 2, 3, 4, 7, 1, 13, 1, 12, 3, 3, 3, 24, 1, 3, 3, 17, 1, 13, 1, 7, 8, 3, 1, 40, 2, 8, 3, 7, 1, 20, 3, 17, 3, 3, 1, 41, 1, 3, 8, 24, 3, 13, 1, 7, 3, 13, 1, 68, 1, 3, 8, 7, 3, 13, 1, 40, 8, 3, 1, 41, 3, 3, 3, 17, 1, 44, 3, 7, 3, 3, 3 (list; graph; listen)

	OFFSET	`1,7`
	REFERENCES	`HoKyu Lee, Double perfect partitions, Discrete Math., 306 (2006), 519-525.`
	FORMULA	`a(1)=0; a(n)=1 for n=2..5; a(n) = Sum_{m=2..n-1, m-1\|n-1} a(m) for n >= 6.`
	MAPLE	`f:=proc(n) option remember; local t1, m, nm1, mm1; nm1:=n-1; if n <= 1 then RETURN(0); elif n <= 5 then RETURN(1); else t1:=0; for m from 2 to n-1 do mm1:=m-1; if nm1 mod mm1 = 0 then t1:=t1+f(m); fi; od; RETURN(t1); fi; end;`
	CROSSREFS	`Cf. A002033.` `Sequence in context: A055189 A106824 A123508 this_sequence A059660 A035456 A035664` `Adjacent sequences: A117618 A117619 A117620 this_sequence A117622 A117623 A117624`
	KEYWORD	`nonn`
	AUTHOR	`njas, Apr 07 2006`

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Last modified November 18 20:14 EST 2008. Contains 147244 sequences.

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