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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
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
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
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Feb 17 2017
STATUS
approved