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
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