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

1,1

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

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

Crossrefs

Cf. A014574, A085063.

Sequence in context: A196535 A106655 A105313 * A030587 A194764 A194738

Adjacent sequences: A085061 A085062 A085063 * A085065 A085066 A085067

Keyword

nonn

Author

Amarnath Murthy, Jun 28 2003

Extensions

More terms from Robert Israel, May 14 2018

Status

approved