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A238849 Smallest k such that k*n^3 - 1 and k*n^3 + 1 are twin primes. 0
4, 9, 4, 3, 24, 2, 24, 30, 58, 3, 12, 19, 96, 3, 10, 165, 114, 11, 390, 159, 2, 30, 114, 10, 18, 12, 24, 6, 42, 19, 72, 24, 30, 72, 24, 3, 150, 189, 40, 54, 348, 5, 24, 93, 14, 33, 324, 9, 150, 81, 70, 39, 354, 3, 138, 42, 56, 51, 180, 16, 18, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..62.

EXAMPLE

a(1) = 4 because for k = 1, 1*(1^3) - 1 = 0 and 1*(1^3) + 1 = 2 are not twin primes, for k = 2, 1 and 3 are not twin primes, for k = 3, 2 and 4 are not twin primes, so the smallest k that works is k = 4: 4*(1^3) - 1 = 3 and 4*(1^3) + 1 = 5 are twin primes.

PROG

(Python)

import sympy

from sympy import isprime

def f(n):

..for k in range(1, 10**4):

....if isprime(k*(n**3)-1) and isprime(k*(n**3)+1):

......return k

n = 1

while n < 10**3:

..print(f(n))

..n += 1

CROSSREFS

Cf. A071558, A110559.

Sequence in context: A096415 A189510 A281152 * A197582 A086277 A271948

Adjacent sequences:  A238846 A238847 A238848 * A238850 A238851 A238852

KEYWORD

nonn

AUTHOR

Derek Orr, Mar 06 2014

STATUS

approved

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Last modified January 19 15:53 EST 2019. Contains 319307 sequences. (Running on oeis4.)