A199768 -id:A199768 - cp's OEIS frontend

A337674 Numbers k whose prime divisors are all less than or equal to the number of divisors of k.

1, 2, 4, 6, 8, 9, 12, 16, 18, 20, 24, 27, 30, 32, 36, 40, 42, 45, 48, 50, 54, 56, 60, 64, 70, 72, 75, 80, 81, 84, 90, 96, 100, 105, 108, 112, 120, 126, 128, 132, 135, 140, 144, 150, 160, 162, 168, 180, 189, 192, 196, 198, 200, 210, 216, 220, 224, 225, 240, 243, 250

Offset: 1

Richard Peterson, Sep 15 2020

nonn

Density: 33 terms between 1 and 100, 17 between 201 and 300, 11 between 1001 and 1100, and 2 between 1000001 and 1000100.

			42=a(17) is a term, since 2,3 and 7 are the prime divisors of 42, which has 8 divisors. 156=2^2*3*13 is not a term, since 13 is greater than 12, the number of divisors of 156.

A199768 has "strictly less", while this sequence has "less than or equal to".
The union of A199768 and A036878.
A146982 does not include terms 42, 56, 132, 198, 220, 264, 308, 312, 330, ...
Cf. A000005.

Select[Range[250], FactorInteger[#][[-1, 1]] <= DivisorSigma[0, #] &] (* Amiram Eldar, Sep 22 2020 *)

isok(m) = #select(x->(x>numdiv(m)), factor(m)[,1]) == 0; \\ Michel Marcus, Sep 22 2020

cp's OEIS Frontend

A337674 Numbers k whose prime divisors are all less than or equal to the number of divisors of k.

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