a(1)=2. a(n) = the smallest integer > a(n-1) that is not in sequence A137699. A137699(n) = the smallest integer > A137698(n) and not coprime to A137698(n). (A137699(n) = A137698(n) + smallest prime dividing A137698(n).).

Checking for the value of a(17): a(16) = 25. Checking 26, we see that A137699(8) = 26 (because a(8) = 13 and 26 is the smallest integer > 13 that is not coprime to 13). So a(17) does not equal 26. 27, however, does not occur in sequence A137699. So a(17) = 27.