

A099079


Numbers n such that phi(n).phi(n1) ... phi(2).phi(1) is prime(dot between numbers means concatenation).


3




OFFSET

1,1


COMMENTS

Number of digits of primes corresponding to the nine known terms of this sequence are respectively 2,3,9,39,42,44,84,244,441.


LINKS

Table of n, a(n) for n=1..9.
C. Rivera, Primes by Listing, The Prime Puzzles & Problems connection.
Eric Weisstein's World of Mathematics, Integer Sequence Primes


EXAMPLE

9 is in the sequence because phi(9).phi(8).phi(7).phi(6).phi(5).phi(4).phi(3).phi(2).phi(1) = 646242211 is prime.


MATHEMATICA

Module[{nn=210, eph}, eph=EulerPhi[Range[nn]]; Position[Table[FromDigits[ Flatten[ IntegerDigits[Reverse[Take[eph, n]]]]], {n, nn}], _?PrimeQ]]// Flatten (* Harvey P. Dale, Apr 21 2020 *)


CROSSREFS

Cf. A046035, A099077, A099078, A099080.
Sequence in context: A057296 A057248 A015960 * A006797 A144239 A320951
Adjacent sequences: A099076 A099077 A099078 * A099080 A099081 A099082


KEYWORD

base,more,nonn


AUTHOR

Farideh Firoozbakht, Oct 23 2004


STATUS

approved



