A231880 - OEIS

%I #19 Jun 18 2016 09:08:15

%S 0,10,24,3,6,1,8,14,4,9,16,12,15,21,25,2,5,22,45,18,28,81,34,20,29,7,

%T 48,13,27,19,26,11,52,30,42,39,61,33,46,17,23,40,32,49,60,57,64,35,92,

%U 43,36,31,63,54,67,41,38,44,62,47,56,70,65,74,124,69,37

%N The digits of a(n) and a(n+1) together can be reordered to form a square; lexicographically earliest sequence of distinct nonnegative integers with this property.

%C A231880 and A231881 eventually merge: A231880(2540) = 2536; A231881(2539) = 2541; A231880(2541,2542,..) = A231881(2540,2541,..) = 2544,2551; ... _Hans Havermann_, Nov 17 2013

%H Hans Havermann, <a href="/A231880/b231880.txt">Table of n, a(n) for n = 0..10000</a>

%t a[0] = 0; a[n_] := a[n] = Block[{k = 1, idm = IntegerDigits@ a[n - 1], t = a@# & /@ Range[n - 1]}, Label[ start]; While[ MemberQ[t, k], k++]; While[ Select[ Permutations[ Join[idm, IntegerDigits[ k]]], #[[1]] != 0 && IntegerQ[ Sqrt[ FromDigits[ #]]] &] == {}, k++; Goto[ start]]; k]; Array[a, 100, 0] (* _Robert G. Wilson v_, Nov 17 2013 *)

%Y A variant of A228407. Cf. A231881.

%K nonn,base

%O 0,2

%A _N. J. A. Sloane_, Nov 17 2013, based on a posting to the Sequence Fans Mailing List by _Andrew Weimholt_, Nov 12 2013

%E Corrected and extended by _Hans Havermann_, Nov 17 2013

%E More terms added (from b-file) by _Jon E. Schoenfield_, Dec 22 2013