A242203
Numbers n such that n*3^n + 1 is semiprime.
Original entry on oeis.org
1, 3, 10, 16, 20, 22, 24, 34, 39, 56, 63, 108, 128, 194, 202, 212, 214, 218, 314, 364, 662, 722
Offset: 1
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IsSemiprime:=func; [n: n in [1..130] | IsSemiprime(s) where s is n*3^n+1];
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Select[Range[130], PrimeOmega[# 3^# + 1] == 2 &]
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isok(n) = bigomega(n*3^n + 1)==2; \\ Michel Marcus, Mar 30 2019
A216376
Semiprimes of the form n*10^n + 1.
Original entry on oeis.org
201, 500001, 130000000000001, 280000000000000000000000000001, 340000000000000000000000000000000001, 36000000000000000000000000000000000001, 39000000000000000000000000000000000000001
Offset: 1
a(1) = 2 * 10^2 + 1 = 201 = 3 * 67.
a(2) = 5 * 10^5 + 1 = 500001 = 3 * 166667.
a(3) = 13*10^13 + 1 = 130000000000001 = 6529 * 19911165569.
a(4) = 28 * 10^28 + 1 = 29 * 9655172413793103448275862069.
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IsSemiprime:= func; [s: n in [1..40] | IsSemiprime(s) where s is n*10^n + 1]; // Vincenzo Librandi, Sep 22 2012
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SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Table[n*10^n + 1, {n, 50}], SemiPrimeQ[#] &] (* T. D. Noe, Sep 07 2012 *)
Select[Table[n*10^n + 1, {n, 50}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 22 2012 *)
Showing 1-2 of 2 results.
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