cp's OEIS Frontend

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

%I A382072 #6 Mar 17 2025 22:19:30
%S A382072 1,3,2,6,24,4,720,15,80,12,3628800,10,479001600,360,8,45,
%T A382072 20922789888000,40,6402373705728000,36,240,1814400,
%U A382072 1124000727777607680000,5,145152,239500800,13440,180,304888344611713860501504000000,168,265252859812191058636308480000000
%N A382072 Lexicographically earliest sequence of distinct positive integers such that for any n > 0, n*a(n) is a factorial number.
%C A382072 This sequence is a self-inverse permutation of the positive integers.
%H A382072 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%e A382072 The first terms, alongside n*a(n), are:
%e A382072   n   a(n)       n*a(n)
%e A382072   --  ---------  ------
%e A382072    1          1      1!
%e A382072    2          3      3!
%e A382072    3          2      3!
%e A382072    4          6      4!
%e A382072    5         24      5!
%e A382072    6          4      4!
%e A382072    7        720      7!
%e A382072    8         15      5!
%e A382072    9         80      6!
%e A382072   10         12      5!
%e A382072   11    3628800     11!
%e A382072   12         10      5!
%e A382072   13  479001600     13!
%e A382072   14        360      7!
%e A382072   15          8      5!
%Y A382072 Cf. A000142, A007672, A382067.
%K A382072 nonn
%O A382072 1,2
%A A382072 _Rémy Sigrist_, Mar 14 2025