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 A045521 Numbers k such that k! has initial digit '2'. 18
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The asymptotic density of this sequence is log_10(3/2) = 0.176091... (see A154580) (Kunoff, 1987). - Amiram Eldar, Jul 17 2020 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..10000 Sharon Kunoff, N! has the first digit property, The Fibonacci Quarterly, Vol. 25, No. 4 (1987), pp. 365-367. Index entries for sequences related to factorial numbers FORMULA A008905(a(n)) = 2. - 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. Sequence in context: A229238 A212202 A102545 * A338766 A242205 A076434 Adjacent sequences: A045518 A045519 A045520 * A045522 A045523 A045524 KEYWORD nonn,base AUTHOR Jeff Burch EXTENSIONS Offset changed to 1 by Chai Wah Wu, Feb 07 2017 STATUS approved

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Last modified December 1 23:26 EST 2023. Contains 367503 sequences. (Running on oeis4.)