A371050 - OEIS

%I #19 Mar 20 2024 14:41:37

%S 15,42,45,51,123,126,132,135,153,159,366,369,375,378,396,402,405,459,

%T 477,483,1095,1098,1104,1107,1125,1131,1134,1188,1206,1212,1215,1377,

%U 1431,1449,1455,3282,3285,3291,3294,3312,3318,3321,3375,3393,3399,3402,3564

%N Numbers whose ternary representation consists of a run of 1's, then a run of 2's, then a run of 0's.

%C All the numbers are multiples of 3.

%e The ternary representations of 15, 42, 45 are 120, 1120, 1200.

%t Map[#[[1]] &, Select[Map[{#, Map[#[[1]] &, Split[IntegerDigits[#, 3]]] == {1, 2, 0}} &,

%t Range[0, 4000, 3]], #[[2]] &]]  (* this sequence *)

%t Map[IntegerString[#, 3] &, %]  (* A371051 *)

%t (* _Peter J. C. Moses_, Mar 06 2024 *)

%o (Python)

%o from itertools import count, islice

%o def A371050_gen(): # generator of terms

%o     return ((3**b*(3**(l-a)-1>>1)+3**b-1)*3**(a-b) for l in count(3) for a in range(2,l) for b in range(1,a))

%o A371050_list = list(islice(A371050_gen(),20)) # _Chai Wah Wu_, Mar 20 2024

%Y Cf. A007089, A008585, A371051.

%K nonn,base

%O 1,1

%A _Clark Kimberling_, Mar 17 2024