OFFSET
1,3
COMMENTS
Also numbers k such that (10^(k+1)+53)/9 is prime.
2575 also produces a probable prime.
a(20) > 10^5. - Robert Price, Jan 13 2015
a(23) > 670000 (per the Kamada link). - Bill McEachen, Mar 02 2024
LINKS
FORMULA
a(n) = A097684(n) - 1 for all n >= 0. - Rick L. Shepherd, Aug 23 2004
MATHEMATICA
Do[ m = n; If[ primeQ[ 10*(10^n - 1)/9 + 7 ], Print[ n ] ], {n, 1, 1250} ]
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 09 2000
EXTENSIONS
2152 (giving a probable prime) from Rick L. Shepherd, Mar 23 2004
2575 from Rick L. Shepherd, Aug 23 2004
a(16)-a(19) derived from A097684 by Robert Price, Jan 13 2015
a(20)-a(22) from the Kamada link by Bill McEachen, Mar 02 2024
STATUS
approved