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A094534 Centered hexamorphic numbers: the k-th centered hexagonal number, 3k(k-1)+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 (list; graph; refs; listen; history; text; internal format)
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 5-digit term, or 40 or 90 to get a 6-digit term.
LINKS
FORMULA
10^(d-1) <= n < 10^d; 3n(n-1)+1 == n mod 10^d
EXAMPLE
417 is in the sequence because if n=417, 3n(n-1)+1=520417, which ends in 417.
PROG
(PARI) isok(n) = {my(m = 3*n*(n-1)+1); (m - n) % 10^#Str(n) == 0; } \\ Michel Marcus, Jun 21 2018
CROSSREFS
Sequence in context: A262754 A115914 A352616 * A262106 A371715 A081632
KEYWORD
base,easy,nonn
AUTHOR
Robert Munafo, May 07 2004
EXTENSIONS
Name changed by Robert Dawson, Jun 20 2018
STATUS
approved

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Last modified May 24 14:39 EDT 2024. Contains 372778 sequences. (Running on oeis4.)