Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #5 Oct 15 2013 22:32:02
%S 0,2,23,23,547,547,2357,2357,2357,2357,4359293547691,4359293547691,
%T 325798243129564339,325798243129564339,325798243129564339,
%U 325798243129564339,3947306373286437248759663633906484193454376823
%N Fixed points reached when prime-factor-concatenation function [A084317] is started at n!.
%F a(n)=A084318[A000142(n)]=A084318[n! ]
%e n=11: 11!=256.81.25.7.11; a(11)=iter[concatenate[{2,3,5,7,11}]] =A084318[39916800]; the list of iteration:
%e {39916800, 235711, 7151223, 34495309, 41841349, 1116722777, 1958774883, 313113444469, 744730492067, 4359293547691}
%e at each step the ordered prime factors of previous term are concatenated.
%t ffi[x_] := Flatten[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] q[x_] := Apply[Times, Table[Prime[w], {w, 1, x}]] lf[x_] := Length[FactorInteger[x]] nd[x_, y_] := 10*x+y tn[x_] := Fold[nd, 0, x] coc[x_] := Fold[nd, 0, Flatten[IntegerDigits[ba[x]], 1]] Table[FixedPoint[coc, q[w]], {w, 1, 7}]
%Y Cf. A001405, A084317, A084318, A084322.
%K base,nonn
%O 1,2
%A _Labos Elemer_, Jun 20 2003