A264849 a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 23-gonal: (21n^2 - 19n)/2.

1, 30, 648, 6701456, 72020220595275, 970458695858595792221157266, 3377345920936319088412440649783459968197698452784332095, 7477788200541027929765479736500643733301085903714718188060185368351929896324223859775571543015918781111399506

Offset: 1

Author

Anders Hellström, Nov 26 2015

Keywords

• nonn
• base

Examples

			1, 130, 130648 are 23-gonal.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..11
• Wikipedia, Polygonal number

Crossrefs

Cf. A051671, A051875 (23-gonal numbers), A061109, A061110, A261696, A264733, A264738, A264776, A264777, A264842, A264848, A264804.

Programs

PARI

icositrigonal(n)=ispolygonal(n, 23)
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)))

Extensions

a(5)-a(8) from Chai Wah Wu, Mar 15 2018