A264842 a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 13-gonal: (11n^2 - 9n)/2.

1, 3, 36, 54765, 123152388, 374848814886363636, 85794018663817263665487289502938826, 107072047880615405294526336549204869795454545454545454545454545454545466

Offset: 1

Author

Anders Hellström, Nov 26 2015

Keywords

• nonn
• base

Examples

			1, 13, 1336, 133654765 are 13-gonal.
		

Links

• Jon E. Schoenfield, Table of n, a(n) for n = 1..11
• Wikipedia, Polygonal number

Crossrefs

Cf. A051671, A051865 (13-gonal numbers), A061109, A061110, A261696, A264733, A264738, A264776, A264777, A264848, A264849, A264804.

Programs

PARI

tridecagonal(n)=ispolygonal(n, 13)
first(m)=my(s=""); s="1"; print1(1, ", "); for(i=2, m, n=1; while(!tridecagonal(eval(concat(s, Str(n)))), n++); print1(n, ", "); s=concat(s, Str(n)))

Extensions

More terms from Jon E. Schoenfield, Nov 27 2015