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A035065 Numbers k such that k! has a prime number of digits. 3
4, 5, 6, 8, 10, 14, 15, 20, 23, 27, 29, 33, 35, 39, 43, 51, 58, 68, 70, 84, 86, 89, 90, 95, 104, 107, 110, 111, 116, 117, 119, 120, 133, 134, 136, 139, 147, 150, 158, 159, 170, 183, 193, 199, 206, 211, 224, 229, 235, 239, 244, 249, 254, 270, 279, 282, 291, 299 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Index entries for sequences related to factorial numbers

EXAMPLE

a(1)=4 because 4! = 24 has 2 (a prime) digits.

23! = 25852016738884976640000 has exactly 23 digits!

MAPLE

filter:= n -> isprime(1+ilog10(n!)):

select(filter, [$1..1000]); # Robert Israel, Mar 27 2018

MATHEMATICA

Select[ Range[300], PrimeQ[ Floor[ Log[10, #! ] + 1]] & ]

PROG

(PARI) isok(n) = isprime(#digits(n!)); \\ Michel Marcus, Mar 28 2018

(MAGMA) [n: n in [1..300] | IsPrime(Floor(Log(10, Factorial(n))+1))]; // Vincenzo Librandi, Mar 28 2018

CROSSREFS

Cf. A000142, A035066, A067367.

Sequence in context: A274918 A277736 A287358 * A209722 A035067 A027698

Adjacent sequences:  A035062 A035063 A035064 * A035066 A035067 A035068

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Nov 15 1998

EXTENSIONS

Offset corrected by Robert Israel, Mar 27 2018

STATUS

approved

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Last modified November 16 17:39 EST 2018. Contains 317275 sequences. (Running on oeis4.)