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 A247395 #28 Dec 23 2024 14:53:44
%S A247395 1,2,4,10,26,50,122,170,290,362,530,842,962,1370,1682,1850,2210,2810,
%T A247395 3482,3722,4490,5042,5330,6242,6890,7922,9410,10202,10610,11450,11882,
%U A247395 12770,16130,17162,18770,19322,22202,22802,24650,26570,27890,29930,32042,32762
%N A247395 The smallest numbers of every class in a classification of positive numbers (see comment).
%C A247395 Consider a classification of the positive numbers with classes {1}, A000040 (primes), A156759 (n>=2) (preprimes, or preprimes of the first kind), A247393 (preprimes of the second kind), A247394 (preprimes of the third kind), etc.
%C A247395 Then a(0)=1, a(1)=2; for n>=3, a(n) is the smallest number which is a preprime of the (n-1)st kind.
%H A247395 Indranil Ghosh, <a href="/A247395/b247395.txt">Table of n, a(n) for n = 0..1000</a>
%H A247395 Vladimir Shevelev, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2014-September/013643.html">A classification of the positive integers over primes</a>
%F A247395 For n>=3, a(n) = (prime(n-1))^2 + 1.
%t A247395 Table[If[n>2, Prime[n - 1]^2 + 1, 2^n], {n, 0, 43}] (* _Indranil Ghosh_, Mar 08 2017 *)
%o A247395 (PARI) a(n)=if(n>2, (prime(n-1))^2 + 1, 2^n) \\ _Charles R Greathouse IV_, Sep 17 2014
%Y A247395 Cf. A000040, A156759, A247393, A247394.
%K A247395 nonn,easy
%O A247395 0,2
%A A247395 _Vladimir Shevelev_, Sep 16 2014
%E A247395 More terms from _Peter J. C. Moses_, Sep 16 2014