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

1,2

Comments

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

Links

Chai Wah Wu, Table of n, a(n) for n = 1..12

Wikipedia, Heptagonal number

Example

1, 18, 189, 1895296 are heptagonal.

Prog

(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

Crossrefs

Cf. A000566, A264738.

Sequence in context: A115073 A298020 A042393 * A114132 A038704 A229196

Adjacent sequences: A264774 A264775 A264776 * A264778 A264779 A264780

Keyword

nonn,base

Author

Anders Hellström, Nov 24 2015

Extensions

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

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

Status

approved