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A095194
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Least number that yields a semiprime when appended to n!.
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2
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0, 1, 2, 7, 2, 1, 1, 1, 1, 1, 2, 1, 1, 7, 17, 1, 1, 1, 31, 13, 1, 59, 13, 7, 1, 61, 41, 37, 31, 1, 7, 7, 1, 2, 5, 61, 41, 7, 13, 37, 61, 43, 1, 1, 47, 67, 1, 3, 67, 61, 5, 19, 5, 11, 7, 13, 1, 3, 1, 71, 11, 1, 67, 109, 103, 43, 29
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OFFSET
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1,3
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COMMENTS
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a(114) would require the factorization of the 190-digit number 1000*114!+181. - Hugo Pfoertner, May 18 2021
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LINKS
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EXAMPLE
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Refers to the semiprimes 10, 21, 62, 247, 1202, 7201, 50401, 403201, etc.
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MAPLE
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A095194 := proc(n) local nf, i, ns ; nf := convert(n!, base, 10) ; for i from 1 do ns := [op(convert(i, base, 10)), op(nf)] ; add( op(j, ns)*10^(j-1), j=1..nops(ns)) ; if numtheory[bigomega](%) = 2 then return i ; end if; end do: end proc: # R. J. Mathar, Jun 17 2011
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MATHEMATICA
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Array[Block[{m = #!, k = 0}, While[PrimeOmega[10^If[k == 0, 1, IntegerLength[k]]*m + k] != 2, k++]; k] &, 40] (* Michael De Vlieger, May 17 2021 *)
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PROG
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(PARI) a(n)=for(i=0, 1e9, bigomega(eval(Str(n!, i)))==2 & return(i)) \\ M. F. Hasler, Jun 17 2011
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CROSSREFS
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KEYWORD
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base,nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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