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#21 by N. J. A. Sloane at Fri Sep 11 22:26:19 EDT 2020
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#20 by Michael De Vlieger at Fri Sep 11 17:50:13 EDT 2020
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#19 by Michael De Vlieger at Fri Sep 11 17:50:11 EDT 2020
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Tony Crilly, <a href="https://doi.org/10.1017/mag.2020.43">A family of discrete spirals</a>, The Mathematical Gazette (2020) Vol. 104, Issue 560, 215-224.
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| STATUS
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approved
editing
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#18 by Charles R Greathouse IV at Thu Jan 17 13:44:05 EST 2019
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Makoto Kamada, <a href="httphttps://stdkmd.comnet/nrr/1/19991.htm#prime">Prime numbers of the form 199...991</a>.
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Discussion
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| Thu Jan 17
| 13:44
| OEIS Server: https://oeis.org/edit/global/2791
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#17 by N. J. A. Sloane at Tue Apr 21 11:42:20 EDT 2015
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Makoto Kamada, <a href="http://mada.la.coocanstdkmd.jpcom/nrr/1/19991.htm#prime">Prime numbers of the form 199...991</a>.
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Discussion
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| Tue Apr 21
| 11:42
| OEIS Server: https://oeis.org/edit/global/2424
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#16 by Ray Chandler at Tue Nov 04 15:31:08 EST 2014
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#15 by Ray Chandler at Tue Nov 04 15:29:59 EST 2014
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P. Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp191">PDP Reference Table - 191</a>.
Makoto Kamada, <a href="http://mada.la.coocan.jp/nrr/1/19991.htm#prime">FactorizationsPrime numbers of the form 199...991</a>.
<a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
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| FORMULA
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a(n) = A082703(n-21) - 2 for n > 1.
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| CROSSREFS
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Cf. A000533, A002275, A068649, A082703.
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nonn,base,hard,more,changed
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| EXTENSIONS
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Edited by Ray Chandler, Nov 04 2014
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approved
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#14 by Ray Chandler at Tue Nov 04 08:46:20 EST 2014
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#13 by Vincenzo Librandi at Mon Nov 03 03:24:53 EST 2014
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#12 by Vincenzo Librandi at Mon Nov 03 03:24:44 EST 2014
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| MATHEMATICA
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Select[Range[0, 2000], PrimeQ[(180 10^# - 81) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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proposed
editing
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