A377247 - OEIS

A377247

a(n) is the largest k such that the sum of the first k divisors of n is at most n.

1, 1, 1, 2, 1, 3, 1, 3, 2, 3, 1, 4, 1, 3, 3, 4, 1, 4, 1, 4, 3, 3, 1, 6, 2, 3, 3, 5, 1, 6, 1, 5, 3, 3, 3, 6, 1, 3, 3, 6, 1, 6, 1, 5, 5, 3, 1, 7, 2, 5, 3, 5, 1, 6, 3, 6, 3, 3, 1, 9, 1, 3, 5, 6, 3, 6, 1, 5, 3, 6, 1, 9, 1, 3, 5, 5, 3, 6, 1, 8, 4, 3, 1, 9, 3, 3, 3, 6

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OFFSET

1,4

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 1 as the sum of the first divisor of 1 is 1 <= 1 and 1 has no more divisors.

a(6) = 3 as the sum of the first three divisors is 1+2+3 <= 6 but the sum of the first four divisors is 1 + 2 + 3 + 6 = 12 > 6.

MATHEMATICA

A377247[n_] := LengthWhile[Accumulate[Divisors[n]], # <= n &];

Array[A377247, 100] (* Paolo Xausa, Aug 05 2025 *)

PROG