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URL: https://oeis.org/A389763

⇱ A389763 - OEIS

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A389763
First differences of 2-dense numbers.
1
1, 2, 2, 2, 4, 4, 2, 2, 4, 4, 2, 2, 4, 4, 2, 6, 6, 2, 4, 4, 2, 6, 8, 4, 4, 2, 6, 4, 4, 4, 4, 8, 6, 2, 4, 8, 4, 6, 6, 4, 2, 6, 8, 4, 12, 4, 2, 2, 4, 4, 2, 6, 4, 4, 4, 6, 6, 12, 4, 4, 4, 6, 2, 4, 4, 8, 6, 6, 4, 2, 2, 4, 8, 4, 6, 6, 4, 2, 10, 8, 4, 4, 10, 2, 4, 6, 2, 4, 4, 8, 6, 2, 4, 12, 8, 8, 2, 6, 4, 2, 2, 4, 8, 4
OFFSET
1,2
COMMENTS
First differences of A174973.
Also distances between the 1's of A237271.
First differs from A179651 at a(23).
FORMULA
a(n) = A174973(n+1) - A174973(n).
MATHEMATICA
Differences[Select[Range[500], Length[Split[Divisors[#], #2 <= 2*# &]] == 1 &]] (* Paolo Xausa, Oct 23 2025 *)
PROG
(Python)
from itertools import count, islice
from sympy import divisors
def A389763_gen(): # generator of terms
m = 1
for k in count(2):
ds = divisors(k)
for i in range(len(ds)-1):
if (ds[i]<<1)<ds[i+1]:
break
else:
yield k-m
m = k
A389763_list = list(islice(A389763_gen(), 104)) # Chai Wah Wu, Oct 22 2025
CROSSREFS
Cf. A005153, A174973 (2-dense numbers), A179651, A237271.
Sequence in context: A064135 A332476 A179651 * A139560 A192095 A363710
KEYWORD
nonn
AUTHOR
Omar E. Pol, Oct 20 2025
STATUS
approved