A282539 a(1)=1, a(n) is the smallest integer not included earlier such that a(n)*a(n-1)-1 and a(n)*a(n-1)+1 are twin primes.

1, 4, 3, 2, 6, 5, 12, 9, 8, 24, 10, 15, 16, 27, 30, 14, 33, 20, 21, 22, 39, 28, 51, 42, 11, 18, 29, 72, 26, 57, 74, 45, 36, 23, 84, 13, 66, 7, 60, 17, 126, 38, 111, 68, 54, 37, 90, 31, 48, 44, 75, 34, 63, 56, 105, 32, 81, 50, 93, 106, 138, 40, 78, 19, 222, 110, 69, 58

Offset

1,2

Comments

It is only a conjecture that a(n) always exists. - Editors, OEIS, Mar 07 2017

Links

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Prog

(Python)
from sympy import isprime
a = [1]
found = True
while found:
  found = False
  prev = a[len(a)-1]
  for k in range(2, 10001):
    if isprime(prev*k-1) and isprime(prev*k+1) and (k not in a):
      print str(k)+', ',
      a.append(k)
      found = True
      break

Crossrefs

Cf. A000040, A001097, A014574, A073666.

Sequence in context: A260458 A275958 A275957 * A021702 A177037 A010651

Adjacent sequences: A282536 A282537 A282538 * A282540 A282541 A282542

Keyword

nonn

Author

Alex Ratushnyak, Feb 17 2017

Status

approved