OFFSET
1,1
COMMENTS
By the time that n = 10^8 the number of primes <= 10^8 (5761455) exceeds 8*9! (2903040). - Robert G. Wilson v, Jan 16 2002
LINKS
C. Caldwell and G. L. Honaker, Jr., Is pi(6521)=6!+5!+2!+1! unique?, Math. Spectrum, 22:2 (2000/2001) 34-36.
Shyam Sunder Gupta, Fascinating Factorials
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 6521
Eric Weisstein's World of Mathematics, Factorial
EXAMPLE
a(10)=5224903 because there are exactly 5!+2!+2!+4!+9!+0!+3! (or 363035) prime numbers less than or equal to 5224903.
MATHEMATICA
Do[ If[ Apply[ Plus, IntegerDigits[n] ! ] == PrimePi[n], Print[n]], {n, 1, 11100000} ]
PROG
(PARI) isok(n) = my(d=digits(n)); sum(k=1, #d, d[k]!) == primepi(n); \\ Michel Marcus, Nov 07 2018
CROSSREFS
KEYWORD
fini,full,nonn,base
AUTHOR
G. L. Honaker, Jr., Sep 15 1999
STATUS
approved