This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A049529 #24 Mar 19 2025 10:23:16
%S A049529 6500,6501,6510,6511,6521,12066,50372,175677,553783,5224903,5224923,
%T A049529 5246963,5302479,5854093,5854409,5854419,5854429,5854493,5855904,
%U A049529 5864049,5865393,10990544,11071599
%N A049529 Numbers k such that sum of factorials of digits of k equals pi(k) (A000720).
%C A049529 By the time that k = 10^8 the number of primes <= 10^8 (5761455) exceeds 8*9! (2903040). - _Robert G. Wilson v_, Jan 16 2002
%H A049529 C. Caldwell and G. L. Honaker, Jr., <a href="http://www.utm.edu/staff/caldwell/preprints/6521.pdf">Is pi(6521)=6!+5!+2!+1! unique?</a>, Math. Spectrum, 22:2 (2000/2001) 34-36.
%H A049529 Shyam Sunder Gupta, <a href="http://www.shyamsundergupta.com/factorial.htm">Fascinating Factorials</a>
%H A049529 Shyam Sunder Gupta, <a href="https://doi.org/10.1007/978-981-97-2465-9_16">Fascinating Factorials</a>, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 16, 411-442.
%H A049529 G. L. Honaker, Jr. and Chris Caldwell, <a href="https://t5k.org/curios/cpage/992.html">Prime Curios! 6521</a>
%H A049529 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Factorial.html">Factorial</a>
%e A049529 a(10)=5224903 because there are exactly 5!+2!+2!+4!+9!+0!+3! (or 363035) prime numbers less than or equal to 5224903.
%t A049529 Do[ If[ Apply[ Plus, IntegerDigits[n] ! ] == PrimePi[n], Print[n]], {n, 1, 11100000} ]
%o A049529 (PARI) isok(n) = my(d=digits(n)); sum(k=1, #d, d[k]!) == primepi(n); \\ _Michel Marcus_, Nov 07 2018
%Y A049529 Cf. A000720, A049530.
%K A049529 fini,full,nonn,base
%O A049529 1,1
%A A049529 _G. L. Honaker, Jr._, Sep 15 1999