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A238848 Smallest k such that k*n^3 - 1 is prime. 1
3, 1, 2, 2, 4, 2, 14, 7, 6, 2, 4, 4, 14, 3, 4, 2, 16, 4, 12, 9, 2, 5, 16, 2, 2, 3, 16, 6, 10, 4, 2, 4, 22, 2, 6, 3, 6, 10, 6, 3, 22, 5, 2, 3, 4, 2, 18, 4, 26, 10, 4, 5, 6, 2, 2, 7, 6, 2, 10, 5, 2, 9, 4, 2, 16, 3, 6, 9, 2, 3, 30, 5, 14, 6, 24, 5, 16, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..78.

EXAMPLE

a(1) = 3 because for k = 1, 1*(1^3) - 1 = 0 is not prime, for k = 2, 2*(1^3) - 1 = 1 is not prime, but for k = 3, 3*(1^3) - 1 = 2 is prime.

PROG

(Python)

import sympy

from sympy import isprime

def f(n):

..for k in range(1, 10**3):

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

......return k

n = 1

while n < 10**3:

..print(f(n))

..n += 1

CROSSREFS

Cf. A231819, A053989.

Sequence in context: A125266 A002016 A282016 * A117494 A221490 A231819

Adjacent sequences:  A238845 A238846 A238847 * A238849 A238850 A238851

KEYWORD

nonn

AUTHOR

Derek Orr, Mar 06 2014

STATUS

approved

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Last modified January 21 20:06 EST 2019. Contains 319350 sequences. (Running on oeis4.)