This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A118908 #9 Jun 16 2016 03:55:10 %S A118908 4,15,221,48839,2385247913,5689407606470855563, %T A118908 32369358912568429679140929317208046943, %U A118908 1047775396410673232345014594095988998399127191704501568910205139392491645247 %N A118908 a(1) = 4; a(n) is greatest semiprime < a(n-1)^2. %C A118908 Semiprime analog of A059785 a(n+1)=prevprime(a(n)^2), with a(1) = 2. With that, of course, there's always a prime between n and 2n, so a(n) < 2^n. See also A055496 a(1) = 2; a(n) is smallest prime > 2*a(n-1). The obverse of this is A118909 a(1) = 4; a(n) is least semiprime > a(n-1)^2. %C A118908 a(9), which is too large to be included, is equal to a(8)^2-3. - _Giovanni Resta_, Jun 16 2016 %e A118908 a(6) = 32369358912568429679140929317208046943 = 1816568472934912211 * 17818958874845686213 = 5689407606470855563^2 - 26 < a(5)^2. %Y A118908 Cf. A001358, A055496, A076656, A006992, A005384, A005385, A118908-A118913. %K A118908 easy,nonn %O A118908 1,1 %A A118908 _Jonathan Vos Post_, May 05 2006