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Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!) 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 (list; graph; refs; listen; history; text; internal format) OFFSET 1,1 COMMENTS The next term (a(7)) has 95 digits. - Harvey P. Dale, Dec 26 2022 LINKS Table of n, a(n) for n=1..6. Makoto Kamada, Prime numbers of the form 22...223. Index entries for primes involving repunits 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: A093135 A305754 A202997 * A328808 A206763 A306154 Adjacent sequences: A093159 A093160 A093161 * A093163 A093164 A093165 KEYWORD nonn AUTHOR Rick L. Shepherd, Mar 26 2004 EXTENSIONS Edited by Ray Chandler, Feb 27 2012 STATUS approved

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Last modified May 3 18:55 EDT 2024. Contains 372222 sequences. (Running on oeis4.)