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%I #18 Jan 04 2023 17:47:57
%S 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,
%T 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,
%U 4,2,16,3,6,9,2,3,30,5,14,6,24,5,16,5
%N Smallest k such that k*n^3 - 1 is prime.
%H Harvey P. Dale, <a href="/A238848/b238848.txt">Table of n, a(n) for n = 1..1000</a>
%e 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.
%t sk[n_]:=Module[{k=1,n3=n^3},While[!PrimeQ[k*n3-1],k++];k]; Array[sk,80] (* _Harvey P. Dale_, Jan 04 2023 *)
%o (Python)
%o import sympy
%o from sympy import isprime
%o def f(n):
%o ..for k in range(1,10**3):
%o ....if isprime(k*(n**3)-1):
%o ......return k
%o n = 1
%o while n < 10**3:
%o ..print(f(n))
%o ..n += 1
%Y Cf. A231819, A053989.
%K nonn
%O 1,1
%A _Derek Orr_, Mar 06 2014
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