A057678
Primes of the form 2^p - p where p is prime.
Original entry on oeis.org
2, 5, 8179, 524269
Offset: 1
p=3 is prime, and so is 2^p - p = 8 - 3 = 5, so 5 is in the sequence. - _Michael B. Porter_, Jul 19 2016
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a:=proc(n) if isprime(2^ithprime(n)-ithprime(n))=true then 2^ithprime(n)-ithprime(n) else fi end: seq(a(n),n=1..310); # Emeric Deutsch
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lst={};Do[p=Prime[n];If[PrimeQ[p=2^p-p],AppendTo[lst,p]],{n,5!}];lst (* Vladimir Joseph Stephan Orlovsky, Jan 28 2009 *)
Select[Table[2^p-p,{p,Prime[Range[20]]}],PrimeQ] (* Harvey P. Dale, Sep 20 2018 *)
A099409
Numbers k such that 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Original entry on oeis.org
0, 1, 3, 9, 15, 28, 64, 1168, 1695, 2362, 116620, 336405
Offset: 1
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[n: n in [0..1000] | IsPrime( 2*(10^n - 1) div 9 + 5)]; // Vincenzo Librandi, Oct 28 2014
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Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 5], Print[n]], {n, 0, 5000}]
a(11)-a(12) from Kamada data by
Tyler Busby, May 03 2024
A093167
Primes of the form 20*R_k + 7, where R_k is the repunit (A002275) of length k.
Original entry on oeis.org
7, 227, 222222227, 222222222222227, 2222222222222222222222222227, 2222222222222222222222222222222222222222222222222222222222222227
Offset: 1
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Select[FromDigits /@ NestList["2" <> # &, "7", 10^3], PrimeQ] (* Mikk Heidemaa, Nov 18 2015 *)
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list(lim)=for(i=0,lim,m=20*(10^i-1)/9 + 7;if(isprime(m),print1(m," ,"))) \\ Anders Hellström, Nov 18 2015
Showing 1-3 of 3 results.
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