A231922 Working in base 4: a(0)=0, thereafter a(n+1) is the smallest number not already in the sequence such that the bits of a(n) and a(n+1) together can be rearranged to form a palindrome.

0, 11, 1, 10, 100, 12, 2, 20, 101, 22, 3, 13, 31, 103, 30, 110, 33, 111, 21, 102, 120, 201, 210, 1000, 122, 133, 212, 221, 313, 331, 1001, 112, 23, 32, 113, 131, 223, 232, 300, 311, 322, 333, 1003, 123, 132, 213, 231, 312, 321, 1002, 121, 200, 211, 222, 233, 323, 332

Offset

0,2

Comments

This is a permutation of the nonnegative integers in base 4 - see the Comments in A228407 for the proof.

Links

Table of n, a(n) for n=0..56.

Mathematica

a[0] = 0; a[n_] := a[n] = Block[{k = 1, idm = IntegerDigits[ a[n - 1], 4], t = a@# & /@ Range[n - 1]}, Label[ start]; While[ MemberQ[t, k], k++];  While[ Select[ Permutations[ Join[ idm, IntegerDigits[k, 4]]], #[[1]] != 0 && # == Reverse@# &] == {}, k++; Goto[ start]]; k]; s = Array[a, 60, 0]; FromDigits@# & /@ IntegerDigits[s, 4]

Crossrefs

Cf. A230891, A231920, A231924, A231926, A231928, A231930, A231932, A228407, A231923.

Sequence in context: A231932 A231926 A231924 * A231920 A230891 A063431

Adjacent sequences: A231919 A231920 A231921 * A231923 A231924 A231925

Keyword

nonn,base,easy

Author

N. J. A. Sloane and Robert G. Wilson v, Nov 15 2013

Status

approved