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A264777
a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is a heptagonal number (A000566).
7
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
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
Sequence in context: A115073 A298020 A042393 * A114132 A038704 A229196
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