A125838 a(n) is the smallest number m such that k*m - 1 for k=2,3,...,n is prime.
2, 2, 2, 6, 120, 120, 2894220, 397073040, 1236161850, 764907546690, 8955490023480, 138393712627170, 8047290924923250
Offset: 2
Examples
a(7)=120 because 2*120-1, 3*120-1, 4*120-1, 5*120-1, 6*120-1 & 7*120-1 are prime and 120 is the smallest such number.
Links
- Carlos Rivera, Problems & Puzzles.
Programs
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Mathematica
a[n_] := Block[{k=2}, While[! AllTrue[k Range[2, n] - 1, PrimeQ], k += 2]; k]; a /@ Range[2, 8] (* Giovanni Resta, Mar 29 2017 *)
Extensions
a(8) from Luke Pebody (luke.pebody(AT)gmail.com)
a(9)-a(10) from Vladimir Trushkov (vladimir(AT)trushkov.botik.ru)
a(11) from Farideh Firoozbakht
a(5) corrected by and a(12)-a(14) from Giovanni Resta, Mar 29 2017