A396828 - OEIS

%I #8 Jun 11 2026 23:57:48

%S 6,8,10,14,15,21,27,33,35,55,65,77,91,119,133,143,187,209,221,247,299,

%T 323,377,391,437,493,527,551,589,667,713,817,851,899,989,1073,1147,

%U 1189,1247,1271,1333,1457,1517,1591,1739,1763,1927,2021,2173,2279,2419,2491

%N Numbers in A080257 with record low abundancy index.

%C Also numbers with at least 4 divisors that are superdeficient.

%H Hoang Nguyen, <a href="/A396828/b396828.txt">Table of n, a(n) for n = 1..10000</a>

%e a(2) = 8 as 8's abundancy index is (1+2+4+8)/8 = 1.875 < 2, which is 6's abundancy index.

%e a(3) = 10 as 10's abundancy index is (1+2+5+10)/10 = 1.8 < 1.875.

%o (Julia)

%o using Primes

%o function a(n)

%o     num = 1

%o     i = 1

%o     min = 3

%o     while i <= n

%o         num += 1

%o         a_index = sum(divisors(num)) // num

%o         if length(divisors(num)) > 3 && a_index < min

%o             print("$num, ")

%o             min = a_index

%o             i += 1

%o         end

%o     end

%o end

%Y Cf. A004394, A080257, A000040, A001248.

%K nonn

%O 1,1

%A _Hoang Nguyen_, Jun 07 2026