OFFSET
1,2
COMMENTS
For any positive integer k, a(3k) = 0 as any 3k-digit number containing only digits 1 or 4 or both has a digit-sum divisible by 3 and thus the number is divisible by 3. - Rick L. Shepherd, Feb 08 2004
LINKS
Jinyuan Wang, Table of n, a(n) for n = 1..1000
FORMULA
a(3k) = 0 and a(A004023(k)) = (10^A004023(k) - 1)/9 = A004022(k) for all positive integers k. - Rick L. Shepherd, Feb 08 2004
MATHEMATICA
Flatten[Table[Select[FromDigits/@Tuples[{1, 4}, n], PrimeQ, 1], {n, 25}]/.{}->{0}] (* Jinyuan Wang, Mar 09 2020 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Jan 04 1999
EXTENSIONS
More terms from Rick L. Shepherd, Feb 08 2004
STATUS
approved