

A201220


Numbers n such that n, n1, n2 and n3 are 1,2,3,4almost primes respectively.


1



107, 263, 347, 479, 863, 887, 1019, 2063, 2447, 3023, 3167, 3623, 5387, 5399, 5879, 6599, 6983, 7079, 8423, 8699, 9743, 9887, 10463, 11807, 12263, 12347, 14207, 15383, 15767, 18959, 20663, 22343, 23039, 23567, 24239, 27239, 32183, 33647, 33767, 37799
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OFFSET

1,1


COMMENTS

Following a suggestion of Claudio Meller.
n is of the form 12k1, so n2 is a multiple of 3 and n3 is a multiple of 4.


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1700


EXAMPLE

6599 is prime, 6598=2*3299 is semiprime, 6597=3*3*733 is 3almost prime, 6596=2*2*17*97 is 4almost prime.


MATHEMATICA

primeCount[n_] := Plus @@ Transpose[FactorInteger[n]][[2]]; Select[Range[40000], primeCount[#] == 1 && primeCount[#1] == 2 && primeCount[#2] == 3 && primeCount[#3] == 4 &] (* T. D. Noe, Nov 28 2011 *)
Select[Range[40000], PrimeOmega[Range[#, #+3]]=={4, 3, 2, 1}&]+3 (* Harvey P. Dale, Dec 10 2011 *)


PROG

(PARI) list(lim)=my(v=List(), L=(lim2)\3, t); forprime(p=3, L\3, forprime(q=3, min(p, L\p), t=3*p*q+2; if(isprime(t) && isprime((t1)/2) && bigomega(t3)==4, listput(v, t)))); Set(v) \\ Charles R Greathouse IV, Feb 02 2017


CROSSREFS

Subsequence of A005385 and of A201147.
Cf. A005383, A112998, A113000, A113008, A072875, A093552.
Sequence in context: A142914 A089635 A248402 * A088563 A142222 A123300
Adjacent sequences: A201217 A201218 A201219 * A201221 A201222 A201223


KEYWORD

nonn


AUTHOR

Antonio Roldán, Nov 28 2011


STATUS

approved



