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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

Table of n, a(n) for n=1..6.

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 February 18 04:48 EST 2020. Contains 332011 sequences. (Running on oeis4.)