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A076290
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Sum of the semiprime divisors of n.
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3
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0, 0, 0, 4, 0, 6, 0, 4, 9, 10, 0, 10, 0, 14, 15, 4, 0, 15, 0, 14, 21, 22, 0, 10, 25, 26, 9, 18, 0, 31, 0, 4, 33, 34, 35, 19, 0, 38, 39, 14, 0, 41, 0, 26, 24, 46, 0, 10, 49, 35, 51, 30, 0, 15, 55, 18, 57, 58, 0, 35, 0, 62, 30, 4, 65, 61, 0, 38, 69, 59, 0, 19, 0, 74, 40, 42, 77, 71, 0
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| A semiprime is a product of two primes.
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LINKS
| Franklin T. Adams-Watters, Table of n, a(n) for n=1,...,10000
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EXAMPLE
| The divisors of 12 are 1, 2, 3, 4, 6, 12, of which 4 and 6 are semiprime. Hence a(12) = 4 + 6 = 10.
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MATHEMATICA
| isSP[n_] := Module[{f, l}, f = FactorInteger[n]; l = Length[f]; (l == 2 && f[[1]][[2]] == 1 && f[[2]][[2]] == 1) || (l == 1 && f[[1]][[2]] == 2)]; f[n_] := Module[{a, d, l}, a = {}; d = Divisors[n]; l = Length[d]; For[i = 1, i <= l, i++, If[isSP[d[[i]]], a = Append[a, d[[i]]]]]; a]; Table[Apply[Plus, f[i]], {i, 1, 100}]
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PROG
| (PARI) a(n) = local(fn, r, om); fn=factor(n); r=om=0; for(i=1, matsize(fn)[1], om+=fn[i, 1]; r+=fn[i, 1]^2*if(fn[i, 2]==1, -1, 1)); (r+om^2)\2 [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Jul 26 2009]
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CROSSREFS
| Cf. A001358.
Sequence in context: A125961 A016681 A179312 * A198224 A178105 A178109
Adjacent sequences: A076287 A076288 A076289 * A076291 A076292 A076293
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KEYWORD
| easy,nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Nov 24 2002
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