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A065804 Earliest sequence with a(a(n))=n!. 0
1, 1, 2, 4, 6, 7, 24, 120, 9, 40320, 11, 3628800, 13, 479001600, 15, 87178291200, 17, 20922789888000, 19, 6402373705728000, 21, 2432902008176640000, 23, 1124000727777607680000, 720, 26, 15511210043330985984000000, 28 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..27.

Index entries for sequences of the a(a(n)) = 2n family

EXAMPLE

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.

CROSSREFS

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

Sequence in context: A088758 A105176 A061937 * A275693 A135033 A317647

Adjacent sequences:  A065801 A065802 A065803 * A065805 A065806 A065807

KEYWORD

nonn

AUTHOR

Henry Bottomley, Dec 06 2001

STATUS

approved

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Last modified March 21 07:23 EDT 2019. Contains 321367 sequences. (Running on oeis4.)