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A201147 Numbers n such that n, n-1 and n-2 are 1,2,3-almost primes respectively. 2
47, 107, 167, 263, 347, 359, 467, 479, 563, 863, 887, 983, 1019, 1187, 1283, 1907, 2039, 2063, 2099, 2447, 2819, 2879, 3023, 3167, 3203, 3623, 3803, 3947, 4139, 4919, 5387, 5399, 5507, 5879, 6599, 6659, 6983, 7079, 7187, 7523, 7559, 7703, 8423, 8699, 8963 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n-2 is multiple of 3.

n is  of the form 12k-1.

This sequence is subset of A005385.

Following a suggestion of Claudio Meller.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..8400

EXAMPLE

2099 is prime, 2098=2*1049 is semiprime, 2097=3*3*233 is 3-almost prime.

MATHEMATICA

primeCount[n_] := Plus @@ Transpose[FactorInteger[n]][[2]]; Select[Range[10000], primeCount[#] == 1 && primeCount[#-1] == 2 && primeCount[#-2] == 3 &] (* T. D. Noe, Nov 28 2011 *)

Select[Range[10000], PrimeOmega[Range[#, #+2]]=={3, 2, 1}&]+2 (* Harvey P. Dale, Dec 10 2011 *)

PROG

(PARI) list(lim)=my(v=List(), L=(lim-2)\3, t); forprime(p=3, L\3, forprime(q=3, min(p, L\p), t=3*p*q+2; if(isprime(t) && isprime((t-1)/2), listput(v, t)))); Set(v) \\ Charles R Greathouse IV, Feb 01 2017

CROSSREFS

Cf. A005385, A005383, A112998, A113000, A113008, A072875, A093552.

Sequence in context: A216067 A124096 A142796 * A142020 A044234 A044615

Adjacent sequences:  A201144 A201145 A201146 * A201148 A201149 A201150

KEYWORD

nonn

AUTHOR

Antonio Roldán, Nov 27 2011

STATUS

approved

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Last modified July 25 04:48 EDT 2017. Contains 289779 sequences.