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A370919
Positive integers whose ternary representation includes at least one 1, and every 1 is followed by 2.
5
5, 15, 17, 23, 45, 47, 50, 51, 53, 59, 69, 71, 77, 135, 137, 140, 141, 143, 150, 152, 153, 155, 158, 159, 161, 167, 177, 179, 185, 207, 209, 212, 213, 215, 221, 231, 233, 239, 405, 407, 410, 411, 413, 420, 422, 423, 425, 428, 429, 431, 450, 452, 455, 456
OFFSET
1,1
EXAMPLE
The ternary representations of 5, 15, and 17 are 12, 120, and 122.
MATHEMATICA
Map[#[[1]] &, Select[Map[{#, #[[1]] > 0 && #[[1]] == #[[2]] &[{Length[
StringCases[#, "1"]], Length[StringCases[#, "12"]]}] &[
IntegerString[#, 3]]} &, Range[500]], #[[2]] &]] (* Peter J. C. Moses, Mar 05 2024 *)
KEYWORD
nonn,base
AUTHOR
Clark Kimberling, Mar 16 2024
STATUS
approved