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Search: id:A161886
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| A161886 |
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Number of nonzero elements in the n X n Redheffer matrix. |
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+0
4
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| 1, 4, 7, 11, 14, 19, 22, 27, 31, 36, 39, 46, 49, 54, 59, 65, 68, 75, 78, 85, 90, 95, 98, 107, 111, 116, 121, 128, 131, 140, 143, 150, 155, 160, 165, 175, 178, 183, 188, 197, 200, 209, 212, 219, 226, 231, 234, 245, 249, 256, 261, 268, 271, 280, 285, 294, 299, 304
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n)=A006590(n)+A000005(n)-1 [From Barbarel Tres Mil (barbarel3000(AT)yahoo.es), Sep 28 2009]
a(n)=A006218(n)+n-1 [From Barbarel Tres Mil (barbarel3000(AT)yahoo.es), Sep 25 2009]
a(1) = 1, a(n) = a(n-1) + A000005(n) + 1 for n > 1. a(1) = 1, a(n) = A006218(n+1) - A000005(n+1) + n - 1 = A006218(n+1) + A049820(n+1) - 2 = A006590(n+1) - 2 for n > 1. [From Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Nov 08 2009]
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EXAMPLE
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4x4 Redheffer matrix:
1,1,1,1
1,1,0,0
1,0,1,0
1,1,0,1
contains 11 nonzero elements.
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MATHEMATICA
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Contribution from Barbarel Tres Mil (barbarel3000(AT)yahoo.es), Sep 25 2009: (Start)
A161886[n_] := Plus @@ Table[DivisorSigma[0, i], {i, 1, n}] + n - 1
A161886[n_] := Total[Table[ Boole[Divisible[i, j] || (i == 1)], {i, 1, n}, {j, 1, n}], Infinity] (End)
Contribution from Barbarel Tres Mil (barbarel3000(AT)yahoo.es), Sep 28 2009: (Start)
A161889[n_] := Plus @@ Plus @@ Table[Boole[Divisible[i, j] || (i == 1)], {i, 1, n}, {j, 1, n}]
A161889[n_] := Sum[Ceiling[n/i], {i, 1, n}] + DivisorSigma[0, n] - 1 (End)
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CROSSREFS
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Cf. A143104.
Cf. A006590,A000005 [From Barbarel Tres Mil (barbarel3000(AT)yahoo.es), Sep 28 2009]
Sequence in context: A083051 A047345 A087070 this_sequence A003670 A084390 A101741
Adjacent sequences: A161883 A161884 A161885 this_sequence A161887 A161888 A161889
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KEYWORD
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nonn
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AUTHOR
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Mats Granvik (mats.granvik(AT)abo.fi), Jun 21 2009
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EXTENSIONS
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Edited by N. J. A. Sloane, Jun 26 2009
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