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

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

Offset: 1

Author

Vincenzo Librandi, Dec 24 2014

Keywords

• nonn
• more

Comments

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

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

Examples

			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.
		

Links

• FactorDB, Status of 5^766+766

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A252658.

Programs

Magma

IsSemiprime:=func; [m: m in [1..110] | IsSemiprime(s) where s is 5^m+m];

Mathematica

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

PARI

main(m)=select(m->bigomega(5^m + m)==2,vector(m,i,i)); \\ Anders Hellström, Aug 14 2015

Extensions

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

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