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A289287 Starting with a(1) = 1, a(n) = smallest nonnegative integer not yet in the sequence such that the last digit of a(n-1) plus the first digit of a(n) is equal to 9. The digit 0 is not allowed. 2

%I #12 Jul 24 2017 12:54:29

%S 1,8,11,81,82,7,2,71,83,6,3,61,84,5,4,51,85,41,86,31,87,21,88,12,72,

%T 73,62,74,52,75,42,76,32,77,22,78,13,63,64,53,65,43,66,33,67,23,68,14,

%U 54,55,44,56,34,57,24,58,15,45,46,35,47,25,48,16,36,37,26,38,17,27,28,18,19

%N Starting with a(1) = 1, a(n) = smallest nonnegative integer not yet in the sequence such that the last digit of a(n-1) plus the first digit of a(n) is equal to 9. The digit 0 is not allowed.

%C The number of terms of this finite sequence is the ninth central polygonal number, n = 73.

%t Module[{a = {1}, k, d = 9}, TimeConstrained[Do[k = 2; While[Or[MemberQ[a, k], MemberQ[IntegerDigits@ k, 0], # != d] &[Mod[a[[n - 1]], 10] + First@ IntegerDigits@ k], k++]; AppendTo[a, k], {n, 2, 100}], 2]; a] (* _Michael De Vlieger_, Jul 14 2017 *)

%Y Cf. A002061, A289283, A289284, A289285, A289286.

%K nonn,base,fini,full

%O 1,2

%A _Enrique Navarrete_, Jul 01 2017

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)