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

2,1

Links

Table of n, a(n) for n=2..14.

Carlos Rivera, Problems & Puzzles.

Example

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.

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 *)

Crossrefs

Cf. A125839, A088651, A088250.

Sequence in context: A098920 A270557 A129365 * A021453 A053789 A115596

Adjacent sequences: A125835 A125836 A125837 * A125839 A125840 A125841

Keyword

hard,more,nonn

Author

Carlos Rivera, Jan 01 2007

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

Status

approved