id:A123709 - OEIS Search Results

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a(n) = number of nonzero elements in row n of triangle A123706.

+0
7

1, 2, 3, 4, 3, 4, 3, 4, 4, 6, 3, 8, 3, 6, 7, 4, 3, 8, 3, 8, 7, 6, 3, 8, 4, 6, 4, 8, 3, 11, 3, 4, 7, 6, 7, 8, 3, 6, 7, 8, 3, 11, 3, 8, 8, 6, 3, 8, 4, 8, 7, 8, 3, 8, 7, 8, 7, 6, 3, 16, 3, 6, 8, 4, 7, 12, 3, 8, 7, 14, 3, 8, 3, 6, 8, 8, 7, 12, 3, 8, 4, 6, 3, 16, 7, 6, 7, 8, 3, 16, 7, 8, 7, 6, 7, 8, 3, 8, 8, 8, 3, 12 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`Triangle A123706 is the matrix inverse of triangle A010766, where A010766(n,k) = [n/k]. a(n) = 4 when n is in A123710. a(n) = 8 when n is in A123711. a(n) = 16 when n is in A123712.`
	FORMULA	`a(n) = 2^(m+1) - 1 when n is an odd number with exactly m distinct prime factors.`
	EXAMPLE	`a(n) = 3 when n is an odd prime.` `a(n) = 7 when n is an odd number with exactly 2 distinct prime factors (A046388).` `a(n) = 15 when n is an odd number with exactly 3 distinct prime factors (A046389).`
	PROGRAM	`(PARI) {a(n)=local(M=matrix(n, n, r, c, if(r>=c, floor(r/c)))^-1); sum(k=1, n, if(M[n, k]==0, 0, 1))}`
	CROSSREFS	`Cf. A123706, A123707, A123708, A123710, A123711, A123712; A010766.` `Sequence in context: A106826 A139048 A158515 this_sequence A165482 A099034 A165576` `Adjacent sequences: A123706 A123707 A123708 this_sequence A123710 A123711 A123712`
	KEYWORD	`nonn`
	AUTHOR	`Paul D. Hanna (pauldhanna(AT)juno.com), Oct 09 2006`

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Last modified November 30 13:13 EST 2009. Contains 167758 sequences.

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