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 A099078 Numbers k such that pi(k).pi(k-1) ... pi(3).pi(2) is prime (dot between numbers means concatenation). 3
 5, 22, 48, 317, 734, 5235 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Number of digits of primes corresponding to the five known terms of this sequence are respectively 4, 21, 67, 605, 1633. LINKS C. Rivera, Primes by Listing, The Prime Puzzles & Problems connection. Eric Weisstein Integer Sequence Primes EXAMPLE 5 is in the sequence because pi(5).pi(4).pi(3).pi(2) = 3221 is prime. MAPLE r:= 1: v:= 1: Res:= NULL: for k from 3 to 6000 do    if isprime(k) then r:= r+1 fi;    v:= v + r*10^(1+ilog10(v));    if isprime(v) then Res:= Res, k fi od: Res; # Robert Israel, Nov 20 2018 MATHEMATICA s = ""; Do[s = ToString[PrimePi[n]] <> s; k = ToExpression[s]; If[PrimeQ[k], Print[n]], {n, 2, 5235}] (* Ryan Propper, Aug 30 2005 *) CROSSREFS Cf. A046035, A099077, A099079, A099080. Sequence in context: A082005 A273024 A273121 * A272836 A273575 A272848 Adjacent sequences:  A099075 A099076 A099077 * A099079 A099080 A099081 KEYWORD base,more,nonn AUTHOR Farideh Firoozbakht, Oct 23 2004 EXTENSIONS One more term from Ryan Propper, Aug 30 2005 STATUS approved

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Last modified August 11 03:22 EDT 2020. Contains 336421 sequences. (Running on oeis4.)