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A103062
Numbers n such that 7*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
0, 1, 3, 237, 243, 351, 967, 1843, 7405, 9633, 59821
OFFSET
1,3
COMMENTS
Also numbers n such that (68*10^n + 31)/9 is prime.
a(12) > 10^5. - Robert Price, Oct 03 2015
FORMULA
a(n) = A101146(n-1) + 1 for n>1.
EXAMPLE
For n=0, (68*10^n + 31)/9 = 11 which is a prime, so 0 is a term.
MATHEMATICA
Do[ If[ PrimeQ[(68*10^n + 31)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A299836 A299725 A278318 * A157723 A342631 A142730
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(1)=0 inserted and a(11) added by Robert Price, Oct 03 2015
STATUS
approved