A004153 Factorial numbers written backwards.

1, 1, 2, 6, 42, 21, 27, 405, 2304, 88263, 88263, 861993, 6100974, 80207226, 219287178, 8634767031, 88898722902, 690824786553, 8275073732046, 238804001546121, 466718002092342, 4490717124909015, 867067777270004211, 4667948883761025852, 63934932337104844026

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..500

Crossrefs

Cf. A000142, A004086, A004192.

Programs

Maple

a:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||(n!)):
seq(a(n), n=0..30);  # Alois P. Heinz, Apr 09 2015

PARI

reverse(expr)=my(v=Vec(Str(expr)),n=length(v));eval(concat(vector(n,i,v[n-i+1])));
a(n) = reverse(n!); \\ Michel Marcus, Apr 05 2014

Formula

a(n) = A004086(A000142(n)). - Michel Marcus, Apr 05 2014

Extensions

More terms from Eric M. Schmidt, Apr 04 2014