Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #14 Dec 30 2024 04:27:41
%S 162,242,291,371,461,515,2419,2815,11874,64751,81927,264961,276184,
%T 757155,2537825,7717729,9548491,14738827,19728438,19728446,19728464,
%U 23695527,77362954,269776516,269776523,269776532,358399327,2385883646,59955748691,67893872935,848472784869
%N Numbers n such that pi(n)=prime(d_1*d_2*...*d_k) where d_1 d_2 ... d_k is the decimal expansion of n.
%C A107121 is a subsequence of this sequence (see the comments line of A107121).
%C a(32) > 7*10^14, if it exists. - _Giovanni Resta_, Jun 01 2020
%C The sequence is finite as pi(n) >= pi(10^(k-1)) grows faster than prime(9^k) >= prime(d_1*d_2*...*d_k). - _Max Alekseyev_, Dec 30 2024
%e 23695527 is in the sequence because pi(23695527)=prime(2*3*6*9*5*5*2*7).
%t Do[h = IntegerDigits[m]; l = Length[h]; If[Min[h] > 0 && PrimePi[m] == Prime[Product[h[[k]], {k, l}]], Print[m]], {m, 52000000}]
%Y Cf. A097223, A107121.
%K nonn,base,fini,changed
%O 1,1
%A _Farideh Firoozbakht_, May 13 2005
%E a(23)-a(28) from _Donovan Johnson_, Jul 12 2010
%E a(29)-a(31) from _Giovanni Resta_, Jun 01 2020