A085064 a(n) = smallest k such that nk-1 as well as n+k are primes.

4, 3, 2, 1, 6, 1, 6, 3, 2, 3, 12, 1, 18, 3, 2, 3, 6, 1, 12, 3, 2, 9, 6, 7, 6, 15, 2, 3, 12, 1, 30, 15, 4, 3, 12, 5, 24, 3, 8, 21, 12, 1, 18, 3, 2, 57, 6, 5, 12, 3, 2, 9, 6, 5, 12, 3, 2, 3, 42, 1, 18, 9, 4, 3, 6, 7, 6, 15, 2, 27, 18, 1, 66, 15, 8, 3, 6, 5, 120, 3, 8, 15, 18, 5, 12, 3, 2, 15, 18

Offset: 1

Author

Amarnath Murthy, Jun 28 2003

Keywords

• nonn

Comments

a(n)=1 if and only if n is in A014574. - Robert Israel, May 14 2018

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A014574, A085063.

Programs

Maple

f:= proc(n) local k;
for k from 1+(n mod 2) by 2 do
  if isprime(n+k) and isprime(n*k-1) then return k fi
od
end proc:
map(f, [$1..100]); # Robert Israel, May 14 2018

Extensions

More terms from Robert Israel, May 14 2018