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URL: https://oeis.org/A328727

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A328727
Nonnegative numbers whose base-3 expansion has no two consecutive nonzero digits.
4
0, 1, 2, 3, 6, 9, 10, 11, 18, 19, 20, 27, 28, 29, 30, 33, 54, 55, 56, 57, 60, 81, 82, 83, 84, 87, 90, 91, 92, 99, 100, 101, 162, 163, 164, 165, 168, 171, 172, 173, 180, 181, 182, 243, 244, 245, 246, 249, 252, 253, 254, 261, 262, 263, 270, 271, 272, 273, 276
OFFSET
1,3
COMMENTS
This sequence is a ternary variant of A003714, the fibbinary numbers.
Apparently, A122983 gives the distinct values of the first differences of this sequence.
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10923 (Terms < 3^13)
EXAMPLE
The first terms, alongside their ternary representation, are:
n a(n) ter(a(n))
-- ---- ---------
1 0 0
2 1 1
3 2 2
4 3 10
5 6 20
6 9 100
7 10 101
8 11 102
9 18 200
10 19 201
11 20 202
12 27 1000
PROG
(PARI) is(n, base=3) = my (d=digits(n, base)); for (i=1, #d-1, if (d[i] && d[i+1], return (0))); return (1)
(Python)
from itertools import count, islice
from gmpy2 import digits
def A328727_gen(startvalue=0): # generator of terms >= startvalue
for n in count(max(startvalue, 0)):
s = digits(n, 3)
for i in range(len(s)-1):
if '0' not in s[i:i+2]:
break
else:
yield n
A328727_list = list(islice(A328727_gen(), 30)) # Chai Wah Wu, Jan 24 2022
CROSSREFS
Sequence in context: A007086 A047404 A133555 * A032938 A188323 A090892
KEYWORD
nonn,base,easy
AUTHOR
Rémy Sigrist, Oct 26 2019
STATUS
approved