cp's OEIS Frontend

A289667 Concatenate prime factorization written in base 3, convert back to decimal.

%I A289667 #15 Aug 05 2017 12:42:27
%S A289667 1,2,3,8,5,21,7,21,11,23,11,75,13,25,32,22,17,65,19,77,34,65,23,192,
%T A289667 17,67,30,79,29,194,31,23,92,71,52,227,37,73,94,194,41,196,43,227,104,
%U A289667 77,47,201,23,71,98,229,53,192,146,196,100,191,59,680,61,193,106,24
%N A289667 Concatenate prime factorization written in base 3, convert back to decimal.
%C A289667 A080670 is the base 10 version, A230625 is the binary version.
%H A289667 Michael De Vlieger, <a href="/A289667/b289667.txt">Table of n, a(n) for n = 1..10000</a>
%p A289667 # take ifsSorted from A080670
%p A289667 A289667 := proc(n)
%p A289667     local Ldgs, p,eb,pb,b ;
%p A289667     b := 3;
%p A289667     if n = 1 then
%p A289667         return 1;
%p A289667     end if;
%p A289667     Ldgs := [] ;
%p A289667     for p in ifsSorted(n) do
%p A289667         pb := convert(op(1,p),base,b) ;
%p A289667         Ldgs := [op(pb),op(Ldgs)] ;
%p A289667         if op(2, p) > 1 then
%p A289667             eb := convert(op(2,p),base,b) ;
%p A289667             Ldgs := [op(eb),op(Ldgs)] ;
%p A289667         end if;
%p A289667     end do:
%p A289667     add( op(e,Ldgs)*b^(e-1),e=1..nops(Ldgs)) ;
%p A289667 end proc:
%p A289667 seq(A289667(n),n=1..30) ; # _R. J. Mathar_, Aug 05 2017
%t A289667 Table[FromDigits[#, 3] &@ Flatten@ Map[IntegerDigits[#, 3] &, FactorInteger[n] /. {p_, e_} /; p > 0 :> If[e == 1, p, {p, e}]], {n, 64}] (* _Michael De Vlieger_, Jul 29 2017 *)
%o A289667 (PARI) a(n) = {if (n==1, return(1)); f = factor(n); s = []; for (i=1, #f~, s = concat(s, digits(f[i, 1], 3)); if (f[i, 2] != 1, s = concat(s, digits(f[i, 2], 3))););  fromdigits(s, 3);} \\ _Michel Marcus_, Jul 27 2017
%Y A289667 Cf. A080670, A195264, A230625, A230627.
%K A289667 nonn,base
%O A289667 1,2
%A A289667 _N. J. A. Sloane_, Jul 27 2017
%E A289667 More terms from _Michel Marcus_, Jul 27 2017