A252795 Numbers m such that 10^m + m is a semiprime.

3, 7, 37, 43, 49, 51, 57, 73, 127

Offset: 1

Author

Vincenzo Librandi, Dec 27 2014

Keywords

• nonn
• more
• hard

Comments

a(10) >= 217. - Hugo Pfoertner, Aug 06 2019

574 and 601 are also terms in this sequence. - Kevin P. Thompson, May 02 2022

Examples

			3 is in this sequence because 10^3+3 = 17*59 is semiprime.
7 is in this sequence because 10^7+7 = 941*10627 and these two factors are prime.
		

Links

• factordb.com, Status of 10^217+217.

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A089379, A252663.

Programs

Magma

IsSemiprime:=func; [m: m in [1..70] | IsSemiprime(s) where s is 10^m+m];

Mathematica

Select[Range[70], PrimeOmega[10^# + #]==2 &]

PARI

is(n)=bigomega(10^n + n)==2 \\ Anders Hellström, Aug 15 2015

Extensions

a(8) from Carl Schildkraut, Aug 15 2015

Missing a(8) term added by Kevin P. Thompson, May 02 2022