The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A351826 a(n) is the least k such that there are exactly n positive numbers j such that k - 2^j and k + 2^j are both prime. 1
 1, 5, 9, 15, 75, 165, 16065, 137445, 540645, 2222535, 374958045, 18327149295 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS All terms are odd. If the number j is allowed to be 0, then a(1) = 4. - Chai Wah Wu, Mar 24 2022 LINKS Table of n, a(n) for n=0..11. EXAMPLE a(4) = 75 because 75 +/- 2^2 = 79 and 71, 75 +/- 2^3 = 83 and 67, 75 +/- 2^5 = 107 and 43, and 75 +/- 2^6 = 139 and 11 are all prime, and 75 is the least number for which there are exactly 4 such powers of 2. MAPLE f:= proc(n) local t, s: nops(select(t -> isprime(n+2^t) and isprime(n-2^t), [\$1..ilog2(n)])); end proc: V:= Array(0..10): count:= 0: for n from 1 while count < 11 do v:= f(n); if V[v] = 0 then V[v] := n; count:= count+1 fi od: convert(V, list); PROG (Python) from itertools import count from sympy import isprime def A351826(n): for k in count(1, 2): c = 0 for j in count(1): if k-2**j < 2: break if isprime(k-2**j) and isprime(k+2**j): c += 1 if c > n: break if c == n: return k # Chai Wah Wu, Mar 24 2022 CROSSREFS Sequence in context: A249331 A345953 A075133 * A066081 A076856 A242973 Adjacent sequences: A351823 A351824 A351825 * A351827 A351828 A351829 KEYWORD nonn,more AUTHOR J. M. Bergot and Robert Israel, Mar 24 2022 EXTENSIONS a(11) from Jean-Marc Rebert, Mar 31 2022 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 10 09:02 EDT 2024. Contains 375044 sequences. (Running on oeis4.)