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A210321
Number of 4-divided binary words of length n.
2
0, 0, 0, 0, 0, 1, 11, 37, 109, 287, 698, 1617, 3642, 7985, 17208, 36620, 77093, 161027, 334205, 690080, 1418917, 2907655, 5941148, 12110674
OFFSET
1,7
COMMENTS
See A210109 for further information.
REFERENCES
Computed by David Scambler, Mar 19 2012
PROG
(Python)
from itertools import product, combinations, permutations
def is4div(b):
for i, j, k in combinations(range(1, len(b)), 3):
divisions = [b[:i], b[i:j], b[j:k], b[k:]]
all_greater = True
for p, bp in enumerate(permutations(divisions)):
if p == 0: continue
if b >= "".join(bp): all_greater = False; break
if all_greater: return True
return False
def a(n): return sum(is4div("".join(b)) for b in product("01", repeat=n))
print([a(n) for n in range(1, 14)]) # Michael S. Branicky, Aug 27 2021
CROSSREFS
Sequence in context: A075024 A229612 A297797 * A356278 A355630 A306423
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Mar 20 2012
EXTENSIONS
a(18)-a(24) from Michael S. Branicky, Aug 27 2021
STATUS
approved