A065804 - OEIS

%I #5 Mar 30 2012 18:51:35

%S 1,1,2,4,6,7,24,120,9,40320,11,3628800,13,479001600,15,87178291200,17,

%T 20922789888000,19,6402373705728000,21,2432902008176640000,23,

%U 1124000727777607680000,720,26,15511210043330985984000000,28

%N Earliest sequence with a(a(n))=n!.

%H <a href="/index/Aa#aan">Index entries for sequences of the a(a(n)) = 2n family</a>

%e a(3)=4 since any lower value would suggest a(a(3)) was not 3!=6. So a(4)=a(a(3))=3!=6. a(5)=7 since any lower value would prevent a(a(5))=5!. a(6)=a(3!)=a(a(a(3)))=a(a(4))=4!=24. a(7)=a(a(5))=5!=120. a(8)=9 since any lower value would prevent a(a(8))=8!. etc.

%Y Cf. A002516, A038752, A054048, A054049, A054790, A054791.

%K nonn

%O 0,3

%A _Henry Bottomley_, Dec 06 2001