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Search: id:A076277
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| A076277 |
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Number of product signs needed to write all the factorizations of n with all factors >1. |
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+0
2
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| 0, 0, 0, 1, 0, 1, 0, 3, 1, 1, 0, 4, 0, 1, 1, 7, 0, 4, 0, 4, 1, 1, 0, 10, 1, 1, 3, 4, 0, 5, 0, 13, 1, 1, 1, 13, 0, 1, 1, 10, 0, 5, 0, 4, 4, 1, 0, 22, 1, 4, 1, 4, 0, 10, 1, 10, 1, 1, 0, 16, 0, 1, 4, 24, 1, 5, 0, 4, 1, 5, 0, 30, 0, 1, 4, 4, 1, 5, 0, 22, 7, 1, 0, 16, 1, 1, 1, 10, 0, 16, 1, 4, 1, 1, 1, 42, 0
(list; graph; listen)
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OFFSET
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1,8
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EXAMPLE
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12 = 3*4 = 2*6 = 2*2*3, 4 product signs are needed, so a(12)=4.
24 = 12*2 = 6*2*2 = 4*3*2 = 3*2*2*2 = 8*3 = 6*4 with 10 multiplies so a(24) = 10.
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MATHEMATICA
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g[1, r_] := g[1, r]={1, 0}; g[n_, r_] := g[n, r]=Module[{ds, i, val}, ds=Select[Divisors[n], 1<#<=r&]; val={0, 0}+Sum[g[n/ds[[i]], ds[[i]]], {i, 1, Length[ds]}]; val+{0, val[[1]]}]; a[1]=0; a[n_] := g[n, n][[2]]-g[n, n][[1]]; a/@Range[97] (* g[n, r] = {c, f}, where c is the number of factorizations of n with factors <= r and f is the total number of factors in them. - Dean Hickerson Oct 10 2002 *)
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PROGRAM
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(PARI) a(n, k=0)=if(k<=0, a(n, 2)[2], if(n<=1|k>n, [0, 0], [1, 0]+sumdiv(n, d, if(d>=max(2, k)&d<=n/d, a(n/d, d)*[1, 1; 0, 1], [0, 0]))))
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CROSSREFS
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a(n)=A066637(n) - A001055(n) for n>1. - Henry Bottomley, Oct 10 2002.
Sequence in context: A058395 A035694 A006941 this_sequence A130115 A130160 A124801
Adjacent sequences: A076274 A076275 A076276 this_sequence A076278 A076279 A076280
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KEYWORD
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nonn
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AUTHOR
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Remco van Sabben (pvsabben(AT)stwillibrord.nl), Oct 04 2002
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com) and Michael Somos, Oct 08 2002
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