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Search: id:A127542
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| A127542 |
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Number of subsets of {1,2,3,...,n} whose sum is prime. |
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+0
3
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| 0, 2, 4, 7, 12, 22, 42, 76, 139, 267, 516, 999, 1951, 3824, 7486, 14681, 28797, 56191, 108921, 210746, 410016, 804971, 1591352, 3153835, 6249154, 12380967, 24553237, 48731373, 96622022, 191012244, 376293782, 739671592, 1454332766, 2867413428
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..100
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EXAMPLE
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The subsets of {1,2,3} that sum to a prime are {1,2}, {2}, {3}, {2,3}. Thus a(3)=4.
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MAPLE
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with(combinat): a:=proc(n) local ct, pn, j:ct:=0: pn:=powerset(n): for j from 1 to 2^n do if isprime(add(pn[j][i], i=1..nops(pn[j]))) =true then ct:=ct+1 else ct:=ct fi: od: end: seq(a(n), n=1..18);
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MATHEMATICA
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g[n_] := Block[{p = Product[1 + z^i, {i, n}]}, Sum[Boole[PrimeQ[k]]*Coefficient[p, z, k], {k, 0, n*(n + 1)/2}]]; Array[g, 34] (*Chandler*)
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CROSSREFS
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Cf. A053632, A126024.
Sequence in context: A064492 A000072 A018179 this_sequence A023432 A072641 A135360
Adjacent sequences: A127539 A127540 A127541 this_sequence A127543 A127544 A127545
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 03 2007
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Mar 05 2007
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