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%I #12 Aug 20 2017 23:09:34
%S 1,2,3,4,5,6,7,8,9,13,24,35,46,57,68,79,135,246,357,468,579,1357,2468,
%T 3579,13579
%N Positive integers whose digits are in increasing order and whose successive digits differ by exactly 2.
%C There are 11 - 2*k terms of the sequence with k digits, 1 <= k <= 5.
%F The terms can be described by the following linear equations:
%F for 1 <= n <= 9, a(n) = n;
%F for 10 <= n <= 16, a(n) = 11*(n - 9) + 2;
%F for 17 <= n <= 21, a(n) = 111*(n - 16) + 24;
%F for 22 <= n <= 24, a(n) = 1111*(n - 21) + 246;
%F for n = 25, a(n) = 11111*(n - 24) + 2468.
%t Select[Range[10^5], Or[Length@ # == 1, Union@ Differences@ # == {2}] &@ IntegerDigits@ # &] (* _Michael De Vlieger_, Aug 15 2017 *)
%K nonn,base,fini,full
%O 1,2
%A _Enrique Navarrete_, Aug 14 2017
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