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%I #11 Jan 27 2021 05:35:13
%S 10,12,18,20,21,24,27,30,36,40,42,45,48,50,54,60,63,70,72,80,81,84,90,
%T 171,252,414,828,1010,1212,1818,2020,2424,3030,3636,4040,4848,5050,
%U 5454,6060,7070,7272,8080,9090,10101,13131,20202,23232,26262,30303,39393
%N Undulating Harshad numbers: numbers divisible by the sum of their own digits with decimal expansions in an abab...ab pattern.
%C 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
%D Jason Earls, Red Zen, Lulu Press, NY, 2006, pp. 56-57. ISBN: 978-1-4303-2017-3.
%H Amiram Eldar, <a href="/A129120/b129120.txt">Table of n, a(n) for n = 1..2146</a>
%t 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 *)
%Y Cf. A005349, A033619.
%K base,nonn
%O 1,1
%A _Jason Earls_, May 25 2007
%E More terms from _R. J. Mathar_, Jun 15 2007