A252792 Numbers m such that 7^m + m is a semiprime.

2, 3, 6, 12, 15, 16, 30, 54, 244, 850, 1488

Offset

1,1

Links

Table of n, a(n) for n=1..11.

Example

2 is in this sequence because 7^2+2 = 3*17 is semiprime.
6 is in this sequence because 7^6+6 = 5*23531 and these two factors are prime.

Mathematica

Select[Range[600], PrimeOmega[7^# + #]==2 &]

Prog

(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..600] | IsSemiprime(s) where s is 7^m+m];

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A252660.

Sequence in context: A329401 A291174 A281110 * A284638 A111271 A217647

Adjacent sequences: A252789 A252790 A252791 * A252793 A252794 A252795

Keyword

nonn

Author

Vincenzo Librandi, Dec 25 2014

Extensions

a(9) from Carl Schildkraut, Aug 14 2015

a(10) from Kevin P. Thompson, Apr 25 2022

a(11) from Charles R Greathouse IV, Apr 25 2022

Status

approved