A396828 Numbers in A080257 with record low abundancy index.

6, 8, 10, 14, 15, 21, 27, 33, 35, 55, 65, 77, 91, 119, 133, 143, 187, 209, 221, 247, 299, 323, 377, 391, 437, 493, 527, 551, 589, 667, 713, 817, 851, 899, 989, 1073, 1147, 1189, 1247, 1271, 1333, 1457, 1517, 1591, 1739, 1763, 1927, 2021, 2173, 2279, 2419, 2491

Offset

1,1

Comments

Also numbers with at least 4 divisors that are superdeficient.

Links

Hoang Nguyen, Table of n, a(n) for n = 1..10000

Example

a(2) = 8 as 8's abundancy index is (1+2+4+8)/8 = 1.875 < 2, which is 6's abundancy index.
a(3) = 10 as 10's abundancy index is (1+2+5+10)/10 = 1.8 < 1.875.

Prog

(Julia)
using Primes
function a(n)
    num = 1
    i = 1
    min = 3
    while i <= n
        num += 1
        a_index = sum(divisors(num)) // num
        if length(divisors(num)) > 3 && a_index < min
            print("$num, ")
            min = a_index
            i += 1
        end
    end
end

Crossrefs

Cf. A004394, A080257, A000040, A001248.

Sequence in context: A007422 A030513 A161918 * A294729 A242270 A298252

Adjacent sequences: A396823 A396826 A396827 * A396829 A396830 A396831

Keyword

nonn

Author

Hoang Nguyen, Jun 07 2026

Status

approved