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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, 500, 650, 934, 962
OFFSET
1,2
COMMENTS
a(21) >= 500. - Hugo Pfoertner, Aug 03 2019
From Kevin P. Thompson, Apr 24 2022: (Start)
a(25) >= 1402.
m=1448 is also a term of this sequence. (End)
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[130], PrimeOmega[3^# + #]==2 &]
PROG
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [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
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
a(21)-a(24) from Kevin P. Thompson, Apr 24 2022
STATUS
approved