cp's OEIS Frontend

A139591 A139275(n) followed by 18-gonal number A051870(n+1).

%I A139591 #17 Jul 14 2022 17:24:26
%S A139591 0,1,9,18,34,51,75,100,132,165,205,246,294,343,399,456,520,585,657,
%T A139591 730,810,891,979,1068,1164,1261,1365,1470,1582,1695,1815,1936,2064,
%U A139591 2193,2329,2466,2610,2755,2907,3060,3220,3381,3549,3718,3894,4071,4255,4440,4632
%N A139591 A139275(n) followed by 18-gonal number A051870(n+1).
%C A139591 Sequence found by reading the line from 0, in the direction 0, 9, ... and the line from 1, in the direction 1, 18, ..., in the square spiral whose vertices are the triangular numbers A000217.
%H A139591 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>.
%F A139591 Array read by rows: row n gives 8*n^2 + n, 8*(n+1)^2 - 7*(n+1).
%F A139591 G.f.: -x*(7*x+1)/((x-1)^3*(x+1)). - _Colin Barker_, Oct 16 2012
%F A139591 a(n) = 2*n^2 + (7/2)*n + (3/4)*((-1)^n-1). - _Sean A. Irvine_, Jul 14 2022
%e A139591 Array begins:
%e A139591    0,   1;
%e A139591    9,  18;
%e A139591   34,  51;
%e A139591   75, 100;
%e A139591   ...
%Y A139591 Cf. A000217, A046092, A051870, A139275, A077221, A139592, A139593, A139595, A139596, A139597, A139598.
%Y A139591 Partial sums of A047393.
%K A139591 nonn,easy,tabf
%O A139591 0,3
%A A139591 _Omar E. Pol_, May 03 2008