

A252795


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


1




OFFSET

1,1


COMMENTS

a(9) >= 217.  Hugo Pfoertner, Aug 06 2019


LINKS

Table of n, a(n) for n=1..8.
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 HellstrÃ¶m, Aug 15 2015


CROSSREFS

Cf. similar sequences listed in A252788.
Cf. A089379, A252663.
Sequence in context: A269995 A281093 A199347 * A049493 A260380 A260382
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


STATUS

approved



