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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). 8
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..52.

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: A119650 A193343 A118074 * A255989 A192274 A291319

Adjacent sequences:  A115954 A115955 A115956 * A115958 A115959 A115960

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Feb 02 2006

STATUS

approved

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Last modified October 14 01:36 EDT 2019. Contains 327994 sequences. (Running on oeis4.)