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A264842
a(n) is least number > 0 such that the concatenation of a(1) ... a(n) is 13-gonal: (11n^2 - 9n)/2.
6
1, 3, 36, 54765, 123152388, 374848814886363636, 85794018663817263665487289502938826, 107072047880615405294526336549204869795454545454545454545454545454545466
OFFSET
1,2
LINKS
Jon E. Schoenfield, Table of n, a(n) for n = 1..11
Wikipedia, Polygonal number
EXAMPLE
1, 13, 1336, 133654765 are 13-gonal.
PROG
(PARI) tridecagonal(n)=ispolygonal(n, 13)
first(m)=my(s=""); s="1"; print1(1, ", "); for(i=2, m, n=1; while(!tridecagonal(eval(concat(s, Str(n)))), n++); print1(n, ", "); s=concat(s, Str(n)))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Anders Hellström, Nov 26 2015
EXTENSIONS
More terms from Jon E. Schoenfield, Nov 27 2015
STATUS
approved