A252790 Numbers m such that 5^m + m is a semiprime.

1, 4, 8, 17, 144, 154, 298, 572, 732

Offset

1,2

Comments

a(8) > 413. - Carl Schildkraut, Aug 14 2015

a(10) >= 766. - Kevin P. Thompson, May 01 2022

Links

Table of n, a(n) for n=1..9.

FactorDB, Status of 5^766+766

Example

1 is in this sequence because 5^1+1 = 2*3 is semiprime.
8 is in this sequence because 5^8+8 = 3*130211 and these two factors are prime.

Mathematica

Select[Range[413], PrimeOmega[5^# + #]==2 &]

Prog

(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..110] | IsSemiprime(s) where s is 5^m+m];
(PARI) main(m)=select(m->bigomega(5^m + m)==2, vector(m, i, i)); \\ Anders Hellström, Aug 14 2015

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A252658.

Sequence in context: A296399 A119471 A145779 * A144178 A075558 A312824

Adjacent sequences: A252787 A252788 A252789 * A252791 A252792 A252793

Keyword

nonn,more

Author

Vincenzo Librandi, Dec 24 2014

Extensions

a(5)-a(7) from Carl Schildkraut, Aug 14 2015

a(8)-a(9) from Kevin P. Thompson, May 01 2022

Status

approved