This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A124269 #9 Jun 13 2016 06:53:19 %S A124269 12,18,27,30,50,63,75,78,102,124,130,164,172,175,190,231,246,258,279, %T A124269 286,292,332,345,369,404,418,425,430,435,452,524,539,574,578,606,610, %U A124269 638,652,663,692,722,725,775,782,795,801,854,906,916,927,938,963,969 %N A124269 3-almost primes indexed by primes. %C A124269 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 A124269 Giovanni Resta, <a href="/A124269/b124269.txt">Table of n, a(n) for n = 1..10000</a> %F A124269 a(n) = 3almostprime(prime(n)) = A014612(A000040(n)). %e A124269 a(1) = 3almostprime(prime(1)) = 3almostprime(2) = 12 = 2^2 * 3. %e A124269 a(2) = 3almostprime(prime(2)) = 3almostprime(3) = 18 = 2 * 3^2. %e A124269 a(3) = 3almostprime(prime(3)) = 3almostprime(5) = 27 = 3^3. %p A124269 From _R. J. Mathar_, Oct 15 2010: (Start) %p A124269 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 A124269 := proc(n) A014612(ithprime(n)) ; end proc: seq(A124269(n),n=1..80) ; (End) %t A124269 p3 = Select[Range[1000], PrimeOmega[#] == 3 &]; p3[[Prime@ Range@ PrimePi@ Length@ p3]] (* _Giovanni Resta_, Jun 13 2016 *) %Y A124269 Cf. A000040, A014612, A122824, A124268, A124270. %K A124269 easy,nonn %O A124269 1,1 %A A124269 _Jonathan Vos Post_, Oct 23 2006 %E A124269 More terms from _R. J. Mathar_, Oct 15 2010