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 A163178 #7 Mar 03 2019 02:16:40 %S A163178 2,2,3,2,3,2,3,2,3,2,3,2,5,2,3,3,2,5,2,5,2,3,2,2,7,3,3,5,3,5,2,3,2,3, %T A163178 2,2,5,2,5,3,7,2,3,7,3,2,5,2,5,3,2,3,5,2,3,7,3,2,5,2,5,2,3,2,2,3,5,7, %U A163178 2,7,11,3,2,7,3,3,5,3,3,2,7,2,3,2,7,5,3,2,3,2,5,11,2,5,2,3,2,5,2,2,3,2,7,5 %N A163178 a(n) is the central prime factor of A046339(n). %e A163178 a(8)=2 since A046339(8) = 32 = 2*2*2*2*2. %e A163178 a(9)=3 since A046339(9) = 42 = 2*3*7. %e A163178 a(10)=2 since A046339(10) = 44 = 2*2*11. %e A163178 a(11)=3 since A046339(11) = 45 = 3*3*5. %e A163178 a(12)=2 since A046339(12) = 48 = 2*2*2*2*3. %p A163178 cpr := proc(n) nred := n ; while numtheory[bigomega](nred) > 1 do pf := sort(convert(numtheory[factorset](nred), list)) ; nred := nred/op(1, pf)/op(-1, pf) ; od: nred ; end: %p A163178 A046339 := proc(n) option remember ; if n = 1 then 8 ; else for a from procname(n-1)+1 do if not isprime(a) and numtheory[bigomega](a) mod 2 = 1 then RETURN(a) ; fi; od: fi; end: %p A163178 A163178 := proc(n) cpr(A046339(n)) ; end; seq(A163178(n), n=1..120) ; # _R. J. Mathar_, Jul 25 2009 %Y A163178 Cf. A046339, A162361. %K A163178 nonn %O A163178 1,1 %A A163178 _Juri-Stepan Gerasimov_, Jul 22 2009 %E A163178 More terms from _R. J. Mathar_, Jul 25 2009