OFFSET
1,4
LINKS
Robert Israel, Table of n, a(n) for n = 1..5000
EXAMPLE
a(6) = 3 because with prime(6) = 13 we have 2*2+13 = 17, 2*3+13 = 19 and 2*5+13 = 23 prime.
MAPLE
f:= proc(n) local i, p;
p:= ithprime(n);
numboccur(true, map(isprime, [seq(2*ithprime(i)+p, i=1..n-1)]))
end proc:
map(f, [$1..100]);
MATHEMATICA
a[n_] := Module[{p, q},
p = Prime[n];
q = Select[Range[p-1], PrimeQ];
Count[p + 2 q, _?PrimeQ]];
Table[a[n], {n, 1, 100}] (* Jean-François Alcover, May 16 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, May 28 2021
STATUS
approved