A045521 - OEIS (original) (raw)

2, 4, 16, 20, 23, 30, 32, 34, 39, 44, 47, 54, 58, 68, 75, 85, 86, 87, 113, 114, 115, 126, 135, 142, 148, 153, 159, 163, 168, 172, 180, 184, 188, 195, 205, 208, 211, 214, 217, 220, 223, 226, 234, 237, 242, 247, 252, 257, 262, 269, 276, 278, 287, 289, 302, 304

COMMENTS

The asymptotic density of this sequence is log_10(3/2) = 0.176091... (see A154580) (Kunoff, 1987). - Amiram Eldar, Jul 17 2020

EXAMPLE

4 is a term since 4! = 24 has the initial digit 2.

MATHEMATICA

Select[ Range[ 310 ], IntegerDigits[ #! ] [ [ 1 ] ] == 2 & ]

PROG

(PARI) isok(n) = digits(n!)[1] == 2; \\ Michel Marcus, Feb 07 2017

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. See also A000142, A008905, A154580.

EXTENSIONS

Offset changed to 1 by Chai Wah Wu, Feb 07 2017