

A094534


Centered hexamorphic numbers: the kth centered hexagonal number, 3k(k1)+1, ends in k.


1



1, 7, 17, 51, 67, 167, 251, 417, 501, 667, 751, 917, 1251, 1667, 5001, 5417, 6251, 6667, 10417, 16667, 50001, 56251, 60417, 66667, 166667, 260417, 406251, 500001, 666667, 760417, 906251, 1406251, 1666667, 5000001, 5260417, 6406251, 6666667, 16666667
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OFFSET

1,2


COMMENTS

Given any number in the sequence, if you remove one or more digits from the beginning you always get another number in the sequence. This makes it easy to find higher terms  just take an existing term and try adding a digit (with perhaps additional 0's) at the beginning. For example, to 6251 prepend 5 to get a 5digit term, or 40 or 90 to get a 6digit term.


LINKS



FORMULA

10^(d1) <= n < 10^d; 3n(n1)+1 == n mod 10^d


EXAMPLE

417 is in the sequence because if n=417, 3n(n1)+1=520417, which ends in 417.


PROG

(PARI) isok(n) = {my(m = 3*n*(n1)+1); (m  n) % 10^#Str(n) == 0; } \\ Michel Marcus, Jun 21 2018


CROSSREFS



KEYWORD

base,easy,nonn


AUTHOR



EXTENSIONS



STATUS

approved



