

A261696


a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 17gonal: (15n^2  13n)/2.


6




OFFSET

1,2


COMMENTS

There are some interesting patterns observed in the terms. Terms a(5), a(6), a(9), a(10), a(11), a(12), ... share the same prefix of 6798483...
From terms a(n) for n > 5, there seems to a pattern of how they are constructed from previous terms. a(6) is formed by inserting 3483...3 between the penultimate digit and the last digit of a(5). Then a(7) and (8) do not follow this pattern.
The digits of a(9) and a(6) match until the last digit of a(6). Next, a(10), a(11) and (12) are formed from a(9), a(10) and a(11) resp. by inserting 3483...3. Then this pattern is interrupted by a(13) and a(14), and continue again for a(15) ..., etc.
(End)


LINKS



EXAMPLE

1, 17, 17689, 176896797 are 17gonal.


PROG

(PARI) heptadecagonal(n)=ispolygonal(n, 17)
first(m)=my(s=""); s="1"; print1(1, ", "); for(i=2, m, n=1; while(!heptadecagonal(eval(concat(s, Str(n)))), n++); print1(n, ", "); s=concat(s, Str(n)))


CROSSREFS

Cf. A051671, A051869 (17gonal numbers), A061109, A061110, A264733, A264738, A264776, A264777, A264842, A264848, A264849, A264804.


KEYWORD

nonn,base


AUTHOR



EXTENSIONS



STATUS

approved



