OFFSET
1,1
COMMENTS
2*n*prime(a(n))+prime(a(n)-1) and 2*n*prime(a(n))+prime(a(n)+1) are prime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..910
MAPLE
V:= Vector(60): count:= 0:
q:= 3: r:= 5:
for i from 3 while count < 60 do
p:= q; q:= r; r:= nextprime(r);
for k from 2 by 2 do
if isprime(k*q+p) and isprime(k*q+r) then break fi;
od;
v:= k/2;
if v <= 60 and V[v] = 0 then count:= count+1; V[v]:= i; fi
od:
PROG
(PARI) f(n) = my(p=prime(n), k=1); while (! (isprime(k*p+precprime(p-1)) && isprime(k*p+nextprime(p+1))), k++); k; \\ A340212
a(n) = my(m=3); while (f(m) != 2*n, m++); m; \\ Michel Marcus, Jan 01 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 31 2020
STATUS
approved