1,2

a(8) > 435. - Carl Schildkraut, Aug 14 2015

Table of n, a(n) for n=1..7.

1 is in this sequence because 9^1+1 = 2*5 is semiprime.

5 is in this sequence because 9^5+5 = 2*29527 and these two factors are prime.

Select[Range[435], PrimeOmega[9^# + #]==2 &]

(MAGMA) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..435] | IsSemiprime(s) where s is 9^m+m];

Cf. similar sequences listed in A252788.

Cf. A252662.

Sequence in context: A207979 A129963 A115764 * A328359 A003361 A336433

Adjacent sequences: A252791 A252792 A252793 * A252795 A252796 A252797

nonn,more

Vincenzo Librandi, Dec 27 2014

a(4)-a(7) from Carl Schildkraut, Aug 14 2015

approved