A371056 Numbers whose ternary representation consists of a run of 2's, then a run of 0's, then a run of 1's.

19, 55, 58, 73, 163, 166, 175, 217, 220, 235, 487, 490, 499, 526, 649, 652, 661, 703, 706, 721, 1459, 1462, 1471, 1498, 1579, 1945, 1948, 1957, 1984, 2107, 2110, 2119, 2161, 2164, 2179, 4375, 4378, 4387, 4414, 4495, 4738, 5833, 5836, 5845, 5872, 5953, 6319

Offset

1,1

Comments

a(n) == 1 mod 3 for all n.

Links

Table of n, a(n) for n=1..47.

Mathematica

Map[#[[1]] &, Select[Map[{#, Map[#[[1]] &, Split[IntegerDigits[#, 3]]] == {2, 0, 1}} &, Range[1, 36000, 3]], #[[2]] &]]    (* this sequence *)
ToExpression[Map[IntegerString[#, 3] &, %]] (* A371057 *)
(* Peter J. C. Moses, Mar 06 2024 *)

Prog

(Python)
from itertools import count, islice
def A371056_gen(): # generator of terms
    return (3**(l-a)*(3**a-1)+(3**b-1>>1) for l in count(3) for a in range(1, l-1) for b in range(1, l-a))
A371056_list = list(islice(A371056_gen(), 20)) # Chai Wah Wu, Mar 30 2024

Crossrefs

Cf. A007089, A371057.

Sequence in context: A288144 A051871 A371110 * A044121 A044502 A069131

Adjacent sequences: A371053 A371054 A371055 * A371057 A371058 A371059

Keyword

nonn,base

Author

Clark Kimberling, Mar 22 2024

Status

approved