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

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

Offset

1,1

Comments

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

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

Links

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

factordb.com, Status of 10^217+217.

Example

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.

Mathematica

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

Prog

(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..70] | IsSemiprime(s) where s is 10^m+m];
(PARI) is(n)=bigomega(10^n + n)==2 \\ Anders Hellström, Aug 15 2015

Crossrefs

Cf. similar sequences listed in A252788.

Cf. A089379, A252663.

Sequence in context: A269995 A281093 A199347 * A049493 A260380 A363667

Adjacent sequences: A252792 A252793 A252794 * A252796 A252797 A252798

Keyword

nonn,more,hard

Author

Vincenzo Librandi, Dec 27 2014

Extensions

a(8) from Carl Schildkraut, Aug 15 2015

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

Status

approved