OFFSET
1,1
LINKS
Sean A. Irvine, Table of n, a(n) for n = 1..1000
MATHEMATICA
pd[{a_, b_, c___}]:=Flatten[Table[Select[FromDigits/@Select[Tuples[ {a, b, c}, n], Union[Abs[Differences[#]]]=={4}&], PrimeQ], {n, 11}]]; Union[Join[{2, 3, 5, 7}, pd[{1, 5, 9}], pd[{3, 7}]]] (* Harvey P. Dale, Aug 23 2011 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Apr 15 1999
EXTENSIONS
More terms from Naohiro Nomoto, Jul 28 2001
STATUS
approved