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URL: https://oeis.org/A093162

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A093162
Primes of the form 20*R_k + 3, where R_k is the repunit (A002275) of length k.
3
3, 23, 223, 22222223, 22222222223, 222222222222222222222222222222222223
OFFSET
1,1
COMMENTS
The next term (a(7)) has 95 digits. - Harvey P. Dale, Dec 26 2022
FORMULA
a(n) = (20*10^A056656(n) + 7)/9 = (2*10^A096506(n) + 7)/9.
MATHEMATICA
Select[Table[FromDigits[PadLeft[{3}, n, 2]], {n, 40}], PrimeQ] (* Harvey P. Dale, Dec 26 2022 *)
CROSSREFS
Cf. A002275, A056656 (corresponding k, and count of digits 2 in a(n)), A096506.
Sequence in context: A305754 A202997 A379782 * A328808 A206763 A306154
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Mar 26 2004
EXTENSIONS
Edited by Ray Chandler, Feb 27 2012
STATUS
approved