A202778 Least k such that x*k + 1 produces primes for x = 1..n and composite for x = n + 1.

4, 1, 2, 330, 10830, 25410, 8224860, 512820, 12960606120, 434491727670, 1893245380950, 71023095613470, 878232256181280, 11429352906540438870

Offset: 1

Author

Arkadiusz Wesolowski, Jan 06 2012

Keywords

• more
• nonn

References

• Wacław Sierpiński, Czym sie zajmuje teoria liczb. Warsaw: PW "Wiedza Powszechna", 1957, pp. 88-89.

Crossrefs

Another version of A088250.

Programs

Mathematica

Table[k = 1; While[i = 1; While[i <= n && PrimeQ[i*k + 1], i++]; i <= n || PrimeQ[i*k + 1], k++]; k, {n, 8}]

Extensions

a(14) from Giovanni Resta, Mar 31 2017