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A129120 Undulating Harshad numbers: numbers divisible by the sum of their own digits with decimal expansions in an abab...ab pattern. 1
10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42, 45, 48, 50, 54, 60, 63, 70, 72, 80, 81, 84, 90, 171, 252, 414, 828, 1010, 1212, 1818, 2020, 2424, 3030, 3636, 4040, 4848, 5050, 5454, 6060, 7070, 7272, 8080, 9090, 10101, 13131, 20202, 23232, 26262, 30303, 39393 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
This definition of "undulating" is more restrictive than the one used in A033619 and excludes single-digit numbers and numbers of the pattern aaaaaa. - R. J. Mathar, Jun 15 2007
REFERENCES
Jason Earls, Red Zen, Lulu Press, NY, 2006, pp. 56-57. ISBN: 978-1-4303-2017-3.
LINKS
MATHEMATICA
undHarsQ[n_] := Module[{d = IntegerDigits[n]}, Divisible[n, Plus @@ d] && Length @ Union[d] > 1 && Length @ Union[d[[1 ;; -1 ;; 2]]] == 1 && Length @ Union[d[[2 ;; -1 ;; 2]]] == 1 ]; Select[Range[40000], undHarsQ] (* Amiram Eldar, Jan 27 2021 *)
CROSSREFS
Sequence in context: A247626 A247627 A327709 * A134516 A144363 A051247
KEYWORD
base,nonn
AUTHOR
Jason Earls, May 25 2007
EXTENSIONS
More terms from R. J. Mathar, Jun 15 2007
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)