login
A340210
a(n) is the least k > 0 such that k*prime(n)+prime(n+1) and k*prime(n)+prime(n+2) are both prime.
4
1, 2, 6, 18, 6, 48, 12, 2, 36, 8, 6, 30, 66, 12, 22, 66, 18, 96, 18, 8, 30, 6, 24, 60, 114, 114, 138, 30, 66, 12, 18, 42, 54, 120, 14, 6, 48, 38, 22, 180, 78, 6, 30, 18, 14, 24, 6, 18, 12, 6, 36, 12, 2, 66, 4, 240, 18, 12, 60, 150, 78, 84, 90, 126, 42, 18, 36, 30, 12, 36, 24, 14, 24, 6, 6, 84, 48
OFFSET
1,2
COMMENTS
a(n) is even for n > 1.
a(n) = 2 for n in A340225.
LINKS
EXAMPLE
For n=3, prime(3)=5, prime(4)=7, prime(5)=11, and 6*5+7= 37 and 6*5+11=41 are prime, so a(3)=6.
MAPLE
f:= proc(n) local p, q, r, k;
p:= ithprime(n);
q:= ithprime(n+1);
r:= ithprime(n+2);
for k from 2 by 2 do
if isprime(k*p+q) and isprime(k*p+r) then return k fi
od
end proc:
f(1):= 1:
map(f, [$1..100]);
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 31 2020
STATUS
approved