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A196660
Smallest k>0 such that k*n+(n-1) is prime.
7
2, 1, 1, 1, 3, 1, 1, 2, 1, 1, 3, 1, 7, 2, 1, 1, 3, 2, 1, 2, 1, 1, 5, 1, 5, 3, 1, 2, 5, 1, 1, 3, 3, 1, 3, 1, 1, 2, 5, 1, 3, 1, 5, 2, 1, 2, 5, 3, 1, 2, 1, 1, 3, 1, 1, 2, 1, 2, 5, 2, 7, 6, 3, 1, 5, 1, 5, 3, 1, 1, 3, 4, 13, 5, 1, 1, 3, 2, 1, 2, 7, 1, 3, 1, 5, 2, 1, 2, 15
OFFSET
1,1
COMMENTS
Conjecture: for every n their exists k < n (apart from a(1)) such that k*n+(n-1) is prime. See A034693.
EXAMPLE
If n=13, the smallest prime in the sequence 25,38,51,64,77,90,103,... is 103, so a(13)=7.
MATHEMATICA
q[n_]:=(k=0; While[!PrimeQ[++k*n+n-1]]; k); Table[q[n], {n, 1, 100}]
CROSSREFS
Sequence in context: A138904 A357138 A357180 * A342323 A374433 A135222
KEYWORD
nonn
AUTHOR
Frank M Jackson, Oct 05 2011
STATUS
approved