A264848 a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 19-gonal: (17n^2 - 15n)/2.

1, 9, 224, 631909, 58000804596, 61688194098028272863216, 2514637794509678630513616176470588235294117671, 941048382372874985200592647058823529411764708485294117647058823529411764705882352941176469

Offset: 1

Author

Anders Hellström, Nov 26 2015

Keywords

• nonn
• base

Examples

			1, 19, 19224, 19224631909 are 19-gonal.
		

Links

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

Crossrefs

Cf. A051671, A051871 (19-gonal numbers), A061109, A061110, A261696, A264733, A264738, A264776, A264777, A264804, A264842, A264849.

Programs

PARI

enneadecagonal(n)=ispolygonal(n, 19)
first(m)=my(s=""); s="1"; print1(1, ", "); for(i=2, m, n=1; while(!enneadecagonal(eval(concat(s, Str(n)))), n++); print1(n, ", "); s=concat(s, Str(n)))

Extensions

a(5)-a(8) from Chai Wah Wu, Mar 16 2018