OFFSET
1,3
COMMENTS
Looking at the format 90*k + 67 modulo 9 and modulo 10 we see that all entries of A142323 have digital root 4 and last digit 7. (Reverting the process is an application of the Chinese remainder theorem.)
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
MAPLE
a:= proc(n) option remember; local k;
for k from 1+ `if`(n=1, -1, a(n-1))
while not isprime(90*k+67) do od; k
end:
seq(a(n), n=1..100); # Alois P. Heinz, Dec 06 2011
MATHEMATICA
Select[Range[0, 4000], PrimeQ[90 #+67]&] (* Vincenzo Librandi, Dec 12 2011 *)
PROG
(Magma) [n: n in [0..200] | IsPrime(90*n+67)]; // Vincenzo Librandi, Dec 12 2011
(PARI) is(n)=isprime(90*n+67) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
J. W. Helkenberg, Dec 05 2011
STATUS
approved