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 A090906 #11 Dec 15 2016 10:39:16
%S A090906 1,1,2,4,6,12,20,40,80,160,308,628,1256,2488,5000,9940,19928,39864,
%T A090906 79660,159380,318724,637496,1274980,2549924,5099884,10199748,20399528,
%U A090906 40799020,81598052,163196124,326392240,652784444,1305568896,2611137796
%N A090906 Row lengths of the irregular triangle defined in A090905.
%C A090906 Conjecture: For n > 4 the last term of the n-th group is 2p where p is the largest prime in the (n-1)th group. And these are the Bertrand primes.
%F A090906 For n>4 a(n)= 2*(A006992(n)-A006992(n-1)) - Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004
%t A090906 a = {{1, 1}}; Do[k = Last@ a[[i - 1]]; While[! Divisible[Pochhammer[Total@ a[[i - 1]], k], Pochhammer @@ a[[i - 1]]], k++]; AppendTo[a, {Total@a[[i - 1]], k}], {i, 2, 17}]; Last /@ a (* _Michael De Vlieger_, Dec 15 2016 *)
%Y A090906 Cf. A090904, A090905, A090907.
%K A090906 nonn
%O A090906 1,3
%A A090906 _Amarnath Murthy_, Dec 13 2003
%E A090906 More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004
%E A090906 More terms from _David Wasserman_, Feb 10 2006