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A201147
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Numbers m such that m, m-1 and m-2 are 1,2,3-almost primes respectively.
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2
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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
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OFFSET
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1,1
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COMMENTS
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m-2 is multiple of 3.
m is of the form 12k-1.
This sequence is subset of A005385.
Following a suggestion of Claudio Meller.
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..8400
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EXAMPLE
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2099 is prime, 2098=2*1049 is semiprime, 2097=3*3*233 is 3-almost prime.
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Cf. A005385, A005383, A112998, A113000, A113008, A072875, A093552.
Sequence in context: A124096 A308784 A142796 * A142020 A044234 A044615
Adjacent sequences: A201144 A201145 A201146 * A201148 A201149 A201150
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KEYWORD
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nonn
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AUTHOR
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Antonio Roldán, Nov 27 2011
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STATUS
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approved
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