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 A252788 Numbers m such that 3^m + m is a semiprime. 8
 1, 4, 7, 14, 16, 20, 22, 32, 38, 55, 80, 92, 188, 220, 296, 328, 370, 422, 452, 454 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(21) >= 500. - Hugo Pfoertner, Aug 03 2019 LINKS factordb.com, Status of 3^500+500. EXAMPLE 1 is in this sequence because 3^1+1 = 2*2 is semiprime. 14 is in this sequence because 3^14+14 = 283*16901 and these two factors are prime. MATHEMATICA Select[Range, PrimeOmega[3^# + #]==2 &] PROG (MAGMA) IsSemiprime:=func; [m: m in [1..130] | IsSemiprime(s) where s is 3^m+m]; (PARI) first(m)=my(v=vector(m), r=1); for(i=1, m, while(bigomega(3^r + r)!=2, r++); v[i]=r; r++); v; \\ Anders Hellström, Aug 14 2015 CROSSREFS Cf. numbers m such that k^m+m is a semiprime: A085745 (k=2), this sequence (k=3), A252789 (k=4), A252790 (k=5), A252791 (k=6), A252792 (k=7), A252793 (k=8), A252794 (k=9), A252795 (k=10). Cf. A252656. Sequence in context: A310851 A310852 A072031 * A310853 A310854 A310855 Adjacent sequences:  A252785 A252786 A252787 * A252789 A252790 A252791 KEYWORD nonn,more AUTHOR Vincenzo Librandi, Dec 22 2014 EXTENSIONS a(13)-a(16) from Luke March, Jul 18 2015 a(17)-a(20) from Carl Schildkraut, Aug 19 2015 STATUS approved

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Last modified September 30 03:03 EDT 2020. Contains 337432 sequences. (Running on oeis4.)