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A124269 3-almost primes indexed by primes. 11

%I

%S 12,18,27,30,50,63,75,78,102,124,130,164,172,175,190,231,246,258,279,

%T 286,292,332,345,369,404,418,425,430,435,452,524,539,574,578,606,610,

%U 638,652,663,692,722,725,775,782,795,801,854,906,916,927,938,963,969

%N 3-almost primes indexed by primes.

%C Primes indexed by 3-almostprimes = A124268. prime(3almostprime(n)) - 3almostprime(prime(n)) = A124270. See also A106349 Primes indexed by semiprimes. See also A106350 Semiprimes indexed by primes. See also A122824 Prime(semiprime(n)) - semiprime(prime(n)). Commutator [A000040,A001358] at n.

%H Giovanni Resta, <a href="/A124269/b124269.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = 3almostprime(prime(n)) = A014612(A000040(n)).

%e a(1) = 3almostprime(prime(1)) = 3almostprime(2) = 12 = 2^2 * 3.

%e a(2) = 3almostprime(prime(2)) = 3almostprime(3) = 18 = 2 * 3^2.

%e a(3) = 3almostprime(prime(3)) = 3almostprime(5) = 27 = 3^3.

%p From _R. J. Mathar_, Oct 15 2010: (Start)

%p A014612 := proc(n) option remember; if n = 1 then 8; else for a from procname(n-1)+1 do if numtheory[bigomega](a) = 3 then return a; end if; end do; end if; end proc:

%p A124269 := proc(n) A014612(ithprime(n)) ; end proc: seq(A124269(n),n=1..80) ; (End)

%t p3 = Select[Range[1000], PrimeOmega[#] == 3 &]; p3[[Prime@ Range@ PrimePi@ Length@ p3]] (* _Giovanni Resta_, Jun 13 2016 *)

%Y Cf. A000040, A014612, A122824, A124268, A124270.

%K easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Oct 23 2006

%E More terms from _R. J. Mathar_, Oct 15 2010

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)