This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
See A331204.
for(n=0,14, for(m=n+1,oo, k=2^m-2^n+1; if(isprime(k), print1(k,", "); break)))
a(1) = 2: 2^2 - 2^0 - 1 = 2, thus exponent 2 = A181692(0); a(2) = 5: 2^3 - 2^1 - 1 = 5, 2^2 - 2^1 - 1 = 1 is not a prime, A181692(1) = 3; a(4) = 47: 2^6 - 2^4 - 1 = 31, whereas the first candidate 2^5 - 2^4 - 1 = 15 is composite.
a:=[]; for n in [0..30] do m:=n+1; while not IsPrime(2^m-2^n-1) do m:=m+1; end while; Append(~a,2^m-2^n-1); end for; a; // Marius A. Burtea, Jan 13 2020
f:= proc(n) local m, p;
p:= -1;
for m from n do
p:= p + 2^m;
if isprime(p) then return p fi
od
end proc:
map(f, [$0..30]); # Robert Israel, Jan 13 2020
a[n_] := For[m = n+1, True, m++, If[PrimeQ[p = 2^m-2^n-1], Return[p]]]; a /@ Range[0, 28] (* Jean-François Alcover, Oct 25 2020 *)
for(n=0,28, for(m=n+1,oo, k=2^m-2^n-1; if(isprime(k), print1(k,", "); break)))
Comments