A395004 a(n) is the larger of the two factors whose product is A394991.

1, 3, 6, 14, 30, 62, 117, 217, 467, 979, 1845, 3897, 7793, 15985, 31943, 64711, 129265, 258529, 520673, 849583, 2082753, 4151813, 8357825, 13264529, 33528945, 66985857, 134090689, 268181377, 536616833, 1073496033, 2146467585, 4042815511, 8587869953, 17178943969

Offset

1,2

Comments

The factors may be equal, but no example for n>2 is known.

Links

Table of n, a(n) for n=1..34.

Example

See A394987.

Prog

(Python)
from sympy.utilities.iterables import multiset_permutations
from sympy import divisors
def A395004(n):
    a = 1<<n-1
    b = a<<1
    k = (n<<1)-1
    c = (1<<k+1)-1
    for l in range(k, 0, -1):
        for s in multiset_permutations('0'*l+'1'*(k+1-l)):
            m = c-int(''.join(s), 2)
            for d in divisors(m):
                if d**2>m:
                    break
                if a<=d<b and a*d<=m<b*d:
                    return m//d # Chai Wah Wu, Apr 11 2026

Crossrefs

A395003 is the smaller factor.

Cf. A029837, A394987, A394989, A394990, A394991.

Sequence in context: A308580 A390083 A394990 * A307457 A192672 A396751

Adjacent sequences: A395001 A395002 A395003 * A395005 A395006 A395007

Keyword

nonn

Author

Hugo Pfoertner, Apr 09 2026

Extensions

a(24)-a(34) from Chai Wah Wu, Apr 09 2026

Status

approved