OFFSET
0,2
COMMENTS
Conjecture: a(n) > 0 for all n.
LINKS
Robert Israel, Table of n, a(n) for n = 0..1000
MAPLE
f:= proc(k) local P, i;
P:= select(t -> isprime(t) and isprime(2*k-t) and isprime(-t^2 mod (2*k)), [2, seq(i, i=3..k, 2)]);
nops(P);
end proc:
N:= 60: # for a(0) to a(N)
V:= Array(0..N): count := 0:
for k from 1 while count < N+1 do
v:= f(k);
if v <= N and V[v] = 0 then
count:= count+1;
V[v]:= k;
fi;
od:
convert(V, list);
MATHEMATICA
a[n_] := Count[Select[Range[2, 2*n], PrimeQ], _?(# >= n && PrimeQ[2*n - #] && PrimeQ[Mod[#*(2*n - #), 2*n]] &)]; seq[len_, nmax_] := Module[{s = Table[0, {len}], c = 0, n = 1, i}, While[n < nmax && c < len, i = a[n] + 1; If[i <= len && s[[i]] == 0, c++; s[[i]] = n]; n++]; TakeWhile[s, # > 0 &]]; seq[60, 10^4] (* Amiram Eldar, Dec 30 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 28 2021
STATUS
approved