A264804 a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 11-gonal: (9n^2 - 7n)/2.

1, 1, 526, 64095, 21420730041, 4528059468080555555556, 3834345160635370971474665069772601398563211, 100751687713984558500838936986634939491022212000570658953744730444103042117925197608458

Offset: 1

Author

Anders Hellström, Nov 25 2015

Keywords

• nonn
• base

Links

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

Crossrefs

Cf. A051671, A051682 (11-gonal numbers), A061109, A061110, A261696, A264733, A264738, A264776, A264777, A264842, A264848, A264849.

Programs

PARI

hendecagonal(n)=ispolygonal(n,11)
first(m)=my(v=vector(m),s="");s="1";print1(1, ", ");for(i=2,m,n=1;while(!hendecagonal(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