A252793 Numbers m such that 8^m + m is a semiprime.

1, 3, 5, 7, 11, 15, 21, 25, 75, 107, 221, 257, 273

Offset

1,2

Comments

Next terms: 347?, 479, 521, 551, .... - Charles R Greathouse IV, Aug 17 2015

Links

Table of n, a(n) for n=1..13.

Formula

1 is in this sequence because 8^1+1 = 3*3 is semiprime.

7 is in this sequence because 8^7+7 = 3*699053 and these two factors are prime.

Mathematica

Select[Range[70], PrimeOmega[8^# + #]==2 &]

Prog

(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 8^m+m];
(PARI) is(n)=bigomega(8^n+n)==2 \\ Charles R Greathouse IV, Aug 14 2015

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A252661.

Sequence in context: A333380 A361826 A177139 * A351924 A062488 A316936

Adjacent sequences: A252790 A252791 A252792 * A252794 A252795 A252796

Keyword

nonn

Author

Vincenzo Librandi, Dec 25 2014

Extensions

a(9)-a(10) from Luke March, Jul 26 2015

a(11) from Carl Schildkraut, Aug 14 2015

a(12)-a(13) from Charles R Greathouse IV, Aug 17 2015

Status

approved