OFFSET
1,1
COMMENTS
Variant of repunit primes: each value is 3444...44431, with k-2 4's.
a(28) > 2*10^5. - Robert Price, Jun 07 2016
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 34w31.
EXAMPLE
6 is a term because 3444431 is prime.
8 is a term because 344444431 is prime.
MATHEMATICA
Select[Range[1200], PrimeQ[(31*10^# - 121)/9]&] (* Vladimir Joseph Stephan Orlovsky, Feb 01 2012 *)
PROG
(PARI) is(n)=ispseudoprime((31*10^n - 121)/9) \\ Charles R Greathouse IV, Jun 08 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joao da Silva (zxawyh66(AT)yahoo.com), Oct 31 2005
EXTENSIONS
Edited by Don Reble, Nov 09 2005
a(16) - a(23) from Vladimir Joseph Stephan Orlovsky, Feb 01 2012
a(24) - a(27) from Robert Price, Jun 07 2016
STATUS
approved