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 A189045 #14 Feb 16 2020 00:58:17
%S A189045 15,26,35,143,215,323,511,899,1727,1763,2047,2186,2743,3599,5183,7999,
%T A189045 10403,11663,13823,19043,22499,32399,36863,39203,51983,54871,57599,
%U A189045 72899,79523,97343,121103,157463,176399,186623,213443,238327,248831,272483,279935,324899,359999,381923
%N A189045 Semiprimes which are sub-perfect powers.
%C A189045 Numbers of the form p*q where p and q are primes, not necessarily distinct, such that p*q + 1 is a perfect power (squares, cubes, etc.). In one sense, this is to semiprimes as Mersenne primes A000668 are to primes.
%C A189045 By Catalan's conjecture (or now Mihailescu's theorem), p and q are always distinct. - _T. D. Noe_, Apr 15 2011
%H A189045 T. D. Noe, <a href="/A189045/b189045.txt">Table of n, a(n) for n = 1..8433</a> (terms < 10^12)
%F A189045 A001358 INTERSECTION A045542. A001358 INTERSECTION {A001597 - 1}.
%e A189045 a(9) = 12^3 - 1 = 1727 = 11 * 157.
%t A189045 SemiPrimeQ[n_] := Total[FactorInteger[n]][[2]] == 2; PerfectPowerQ[n_] := GCD @@ Last /@ FactorInteger[n] > 1; Select[Range[400000], SemiPrimeQ[#] && PerfectPowerQ[# + 1] &] (* _T. D. Noe_, Apr 15 2011 *)
%Y A189045 Cf. A001358, A001597, A045542, A177955, A189047.
%K A189045 nonn,easy
%O A189045 1,1
%A A189045 _Jonathan Vos Post_, Apr 15 2011