A115958 Numbers n having exactly 4 distinct prime factors, the largest of which is greater than or equal to sqrt(n) (i.e., sqrt(n)-rough numbers with exactly 4 distinct prime factors).

930, 1110, 1230, 1290, 1410, 1590, 1770, 1806, 1830, 1974, 2010, 2130, 2190, 2226, 2370, 2478, 2490, 2562, 2670, 2814, 2910, 2982, 3030, 3066, 3090, 3210, 3270, 3318, 3390, 3486, 3660, 3738, 3810, 3930, 4020, 4074, 4110, 4170, 4242, 4260, 4326, 4380

Offset

1,1

Links

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

Example

3660 is in the sequence because it has 4 distinct prime factors (2, 3, 5 and 61) and 61 > sqrt(3660).

Maple

with(numtheory): a:=proc(n) if nops(factorset(n))=4 and factorset(n)[4]^2>=n then n else fi end: seq(a(n), n=1..4500);

Mathematica

pf4Q[n_]:=Module[{f=FactorInteger[n]}, Length[f]==4 && f[[-1, 1]] >= Sqrt[ n]]; Select[Range[5000], pf4Q] (* Harvey P. Dale, Sep 13 2017 *)

Crossrefs

Cf. A115956, A115957, A115959, A115960, A115961.

Sequence in context: A219066 A068651 A175726 * A158679 A250384 A209810

Adjacent sequences: A115955 A115956 A115957 * A115959 A115960 A115961

Keyword

nonn

Author

Emeric Deutsch, Feb 02 2006

Status

approved