A382072 Lexicographically earliest sequence of distinct positive integers such that for any n > 0, n*a(n) is a factorial number.

1, 3, 2, 6, 24, 4, 720, 15, 80, 12, 3628800, 10, 479001600, 360, 8, 45, 20922789888000, 40, 6402373705728000, 36, 240, 1814400, 1124000727777607680000, 5, 145152, 239500800, 13440, 180, 304888344611713860501504000000, 168, 265252859812191058636308480000000

Offset

1,2

Comments

This sequence is a self-inverse permutation of the positive integers.

Links

Table of n, a(n) for n=1..31.

Index entries for sequences that are permutations of the natural numbers

Example

The first terms, alongside n*a(n), are:
  n   a(n)       n*a(n)
  --  ---------  ------
   1          1      1!
   2          3      3!
   3          2      3!
   4          6      4!
   5         24      5!
   6          4      4!
   7        720      7!
   8         15      5!
   9         80      6!
  10         12      5!
  11    3628800     11!
  12         10      5!
  13  479001600     13!
  14        360      7!
  15          8      5!

Crossrefs

Cf. A000142, A007672, A382067.

Sequence in context: A356563 A334588 A025240 * A137602 A086550 A266239

Adjacent sequences: A382069 A382070 A382071 * A382073 A382074 A382075

Keyword

nonn

Author

Rémy Sigrist, Mar 14 2025

Status

approved