A045510 Factorials having initial digit '2'.

2, 24, 20922789888000, 2432902008176640000, 25852016738884976640000, 265252859812191058636308480000000, 263130836933693530167218012160000000

Offset: 1

Author

Jeff Burch

Keywords

• nonn
• base

Comments

Benford's law shows that this sequence will contain about (log 3 - log 2)/log 10 =~ 18% of factorials. [Charles R Greathouse IV, Nov 13 2010]

Crossrefs

For factorials with initial digit d (1 <= d <= 9) see A045509, A045510, A045511, A045516, A045517, A045518, A282021, A045519; A045520, A045521, A045522, A045523, A045524, A045525, A045526, A045527, A045528, A045529.

Cf. A000142.

Programs

Mathematica

Select[Range[50]!,IntegerDigits[#][[1]]==2&] (* Harvey P. Dale, Mar 21 2020 *)

PARI

lista(nn) = {for (n=1, nn, if (digits(n!)[1] == 2, print1(n!, ", ")););} \\ Michel Marcus, Dec 13 2017

Formula

a(n) = A000142(A045521(n)). - Amiram Eldar, Jul 19 2020