A264777 a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is a heptagonal number (A000566).

1, 8, 9, 5296, 9701946, 3254409476919, 214948107829163565920446430, 31021083401526077498957998513210666182754941982955902, 81969637737594122848099953820072074027662186843090573669278105078583525219219292274950391247747733666835448

Offset: 1

Author

Anders Hellström, Nov 24 2015

Keywords

• nonn
• base

Comments

a(20) has 219815 decimal digits. - Chai Wah Wu, Nov 25 2015

Examples

			1, 18, 189, 1895296 are heptagonal.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..12
• Wikipedia, Heptagonal number

Crossrefs

Cf. A000566, A264738.

Programs

PARI

isheptagonal(n)=ispolygonal(n,7)
first(m)=my(v=vector(m),s="");s="1";v[1]=1;for(i=2,m,n=1;while(!isheptagonal(eval(concat(s,Str(n)))),n++);v[i]=n;s=concat(s,Str(n)));v

Extensions

a(6)-a(8) from Jon E. Schoenfield, Nov 24 2015

a(9) from Chai Wah Wu, Nov 25 2015