|
%I #27 Mar 17 2018 05:59:07
%S 1,30,648,6701456,72020220595275,970458695858595792221157266,
%T 3377345920936319088412440649783459968197698452784332095,
%U 7477788200541027929765479736500643733301085903714718188060185368351929896324223859775571543015918781111399506
%N a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 23-gonal: (21n^2 - 19n)/2.
%H Chai Wah Wu, <a href="/A264849/b264849.txt">Table of n, a(n) for n = 1..11</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Polygonal_number">Polygonal number</a>
%e 1, 130, 130648 are 23-gonal.
%o (PARI) icositrigonal(n)=ispolygonal(n, 23)
%o first(m)=my(s=""); s="1"; print1(1, ", "); for(i=2, m, n=1; while(!icositrigonal(eval(concat(s, Str(n)))), n++); print1(n, ", "); s=concat(s, Str(n)))
%Y Cf. A051671, A051875 (23-gonal numbers), A061109, A061110, A261696, A264733, A264738, A264776, A264777, A264842, A264848, A264804.
%K nonn,base
%O 1,2
%A _Anders Hellström_, Nov 26 2015
%E a(5)-a(8) from _Chai Wah Wu_, Mar 15 2018
|
