A115957 Numbers n having exactly 3 distinct prime factors, the largest of which is greater than or equal to sqrt(n) (i.e., sqrt(n)-rough numbers with exactly 3 distinct prime factors).

42, 66, 78, 102, 110, 114, 130, 138, 156, 170, 174, 186, 190, 204, 222, 228, 230, 238, 246, 255, 258, 266, 276, 282, 285, 290, 310, 318, 322, 342, 345, 348, 354, 366, 370, 372, 402, 406, 410, 414, 426, 430, 434, 435, 438, 444, 460, 465, 470, 474, 483, 492

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

156 is in the sequence because it has 3 distinct prime factors (2, 3 and 13) and 13 > sqrt(156).

Maple

with(numtheory): a:=proc(n) if nops(factorset(n))=3 and factorset(n)[3]^2>=n then n else fi end: seq(a(n), n=1..530);

Mathematica

Select[Range[500], PrimeNu[#]==3&&FactorInteger[#][[-1, 1]]>=Sqrt[#]&] (* Harvey P. Dale, Apr 09 2019 *)

Crossrefs

Cf. A115956, A115958, A115959, A115960, A115961.

Sequence in context: A193343 A118074 A350641 * A362003 A255989 A192274

Adjacent sequences: A115954 A115955 A115956 * A115958 A115959 A115960

Keyword

nonn

Author

Emeric Deutsch, Feb 02 2006

Status

approved