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A099421
0 together with numbers k such that 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
2
0, 3, 19, 79, 139, 223, 463, 544, 1096, 1419, 3247, 3877, 4417, 9507, 11091, 14602, 27811, 29188, 106729, 188308
OFFSET
1,2
COMMENTS
Also numbers k such that abs(8*10^k - 71)/9 is a prime.
a(19) > 10^5. - Robert Price, Sep 06 2014
FORMULA
a(n) = A056664(n-1) + 1.
MATHEMATICA
Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 7], Print[n]], {n, 0, 15000}]
PROG
(PARI)
for(n=0, 10^4, if(ispseudoprime(abs(8*(10^n-1)/9-7)), print1(n, ", "))) \\ Derek Orr, Sep 06 2014
CROSSREFS
Sequence in context: A240746 A027175 A093734 * A241885 A061171 A293561
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Oct 14 2004
EXTENSIONS
a(17)-a(18) from Kamada data by Robert Price, Sep 06 2014
a(19)-a(20) from Kamada data by Tyler Busby, Apr 30 2024
STATUS
approved