This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A201220 Numbers n such that n, n-1, n-2 and n-3 are 1,2,3,4-almost 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Following a suggestion of Claudio Meller. n is  of the form 12k-1, so n-2 is a multiple of 3 and n-3 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 3-almost prime, 6596=2*2*17*97 is 4-almost 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=(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) && bigomega(t-3)==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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 11 18:34 EST 2019. Contains 329925 sequences. (Running on oeis4.)