OFFSET
1,3
COMMENTS
Also numbers k such that (28*10^k - 1)/9 is prime.
Although perhaps a degenerate case, A002275 defines R(0)=0. Thus zero belongs in this sequence since 3*10^0 + 0 = 3*1 + 0 = 3 is prime. - Robert Price, Oct 28 2014
a(26) > 2*10^5. - Robert Price, Dec 19 2014
LINKS
MATHEMATICA
Do[ If[ PrimeQ[ 3*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
Added zero by Robert Price, Oct 28 2014
a(18)-a(25) from Kamada data by Robert Price, Dec 19 2014
STATUS
approved