A139182 - OEIS

%I #16 Apr 12 2024 16:13:43

%S 50,51,125,15405,26205,226700,226701,226710,226711,513090,513091,

%T 1351832,8210065

%N Numbers m such that pi(m) = d_1!!*d_2!!*...*d_k!! where d_1 d_2 ... d_k is the decimal expansion of m.

%C Numbers m with a product of the double-factorials of the digits equal to A000720(m).

%C If { m is in the sequence, 10 divides m and m+1 is composite } then m+1 is in the sequence. [Clarified by _N. J. A. Sloane_, Feb 06 2022]

%e pi(8210065)=8!!*2!!*1!!*0!!*0!!*6!!*5!!.

%t Select[Range[83*10^5],Times@@(IntegerDigits[#]!!)==PrimePi[#]&] (* _Harvey P. Dale_, Apr 12 2024 *)

%Y Cf. A066457, A006882.

%K base,nonn,less,more

%O 1,1

%A _Farideh Firoozbakht_, Apr 19 2008