A088250
a(n) is the smallest number k such that r*k + 1 is prime for all r = 1 to n.
Original entry on oeis.org
1, 1, 2, 330, 10830, 25410, 512820, 512820, 12960606120, 434491727670, 1893245380950, 71023095613470, 878232256181280, 11429352906540438870
Offset: 1
a(11) = 1893245380950 because all eleven numbers 1*1893245380950 + 1, 2*1893245380950 + 1, 3*1893245380950 + 1, ..., 10*1893245380950 + 1 & 11*1893245380950 + 1 are prime and 1893245380950 is the smallest number with such property.
-
a[n_] := Block[{k = If[n < 4, 1, 6], s}, s = k; While[! AllTrue[k Range[n] + 1, PrimeQ], k += s]; k]; Array[a, 8] (* Giovanni Resta, Mar 31 2017 *)
A088651
a(n) = smallest number k such that rk-1 is prime for all r = 1 to n.
Original entry on oeis.org
3, 3, 4, 6, 6, 154770, 2894220, 2894220, 407874180, 214580145780, 9448481062020, 247236503934420, 2545206711847800, 18178612369988250180, 53792264108455702830
Offset: 1
a(5)=6 because 1*6-1, 2*6-1, 3*6-1, 4*6-1, 5*6-1 are all prime.
a(11)=9448481062020 because all eleven numbers 1*9448481062020-1, 2*9448481062020-1,3*9448481062020-1,...,10*9448481062020-1 & 11*9448481062020-1 are prime and 9448481062020 is the smallest number with such property.
A125838
a(n) is the smallest number m such that k*m - 1 for k=2,3,...,n is prime.
Original entry on oeis.org
2, 2, 2, 6, 120, 120, 2894220, 397073040, 1236161850, 764907546690, 8955490023480, 138393712627170, 8047290924923250
Offset: 2
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.
-
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 *)
a(8) from Luke Pebody (luke.pebody(AT)gmail.com)
a(9)-a(10) from Vladimir Trushkov (vladimir(AT)trushkov.botik.ru)
A164325
a(n) is the smallest number m such that (2k-1)m+1 is prime for all 0
Original entry on oeis.org
1, 2, 2, 6, 1170, 64590, 25153800, 25153800, 4747505070, 207187349040, 6703860240000, 26997529639080, 1760354281625940, 1760354281625940, 10718654377787155800
Offset: 1
a(5) corrected by Zak Seidov, Sep 16 2009
Showing 1-4 of 4 results.
Comments