A036785 Numbers divisible by the squares of two distinct primes.

36, 72, 100, 108, 144, 180, 196, 200, 216, 225, 252, 288, 300, 324, 360, 392, 396, 400, 432, 441, 450, 468, 484, 500, 504, 540, 576, 588, 600, 612, 648, 675, 676, 684, 700, 720, 756, 784, 792, 800, 828, 864, 882, 900, 936, 968, 972, 980, 1000, 1008, 1044

Offset

1,1

Comments

Not squarefree, not a nontrivial prime power and not in {squarefree} times {nontrivial prime powers}.

Numbers k such that A056170(k) > 1. The asymptotic density of this sequence is 1 - (6/Pi^2) * (1 + A154945) = 0.05668359058... - Amiram Eldar, Nov 01 2020

References

CRC Standard Mathematical Tables and Formulae, 30th ed., (1996) page 102-105.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

Select[Range@ 1050, And[Length@ # > 1, Total@ Boole@ Map[# > 1 &, #[[All, -1]]] > 1] &@ FactorInteger@ # &] (* Michael De Vlieger, Apr 25 2017 *)
dstdpQ[n_]:=Length[Select[Sqrt[#]&/@Divisors[n], PrimeQ]]>1; Select[ Range[ 1100], dstdpQ] (* Harvey P. Dale, Jan 15 2020 *)

Prog

(PARI) is(n)=my(f=vecsort(factor(n)[, 2], , 4)); #f>1&&f[2]>1 \\ Charles R Greathouse IV, Nov 15 2012

Crossrefs

Cf. A005117, A025475, A056170, A154945.

Equivalent sequence for 3 distinct primes: A318720.

Cf. A085986, A338539, A339245 (subsequences).

Subsequence of A038838.

Sequence in context: A249726 A335463 A192026 * A338539 A347960 A286708

Adjacent sequences: A036782 A036783 A036784 * A036786 A036787 A036788

Keyword

easy,nonn

Author

Alford Arnold

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Apr 03 2000

New name from Charles R Greathouse IV, Nov 15 2012

Status

approved