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A193226
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Least semiprime whose sum of prime factors equals 2^n.
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1
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4, 15, 39, 87, 183, 2071, 1255, 1527, 3063, 38551, 12279, 106327, 49143, 622231, 1113823, 1703767, 1310695, 9961111, 3145719, 39845527, 12582903, 310377127, 50331639, 2046816631, 335544295, 10603194271, 23890747663, 1610612727, 44023413103
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OFFSET
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2,1
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LINKS
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EXAMPLE
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a(10) = 3063 because 3063 = 3*1021, and 1021 + 3 = 2^10.
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MAPLE
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with(numtheory):for n from 1 to 30 do:x:=2^n:id:=0:for m from 1 to 10000 while(id=0) do:p:=ithprime(m):y:=x-p:if type(y, prime)=true then z:=y*p: id:=1:printf(`%d, `, z): else fi:od:od:
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PROG
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(PARI) a(n)=my(N=2^n); forprime(p=2, default(primelimit), if(isprime(N-p), return(p*(N-p)))) \\ Charles R Greathouse IV, Jul 31 2011
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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