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

1,1

References

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

Links

Table of n, a(n) for n=1..14.

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}]

Crossrefs

Another version of A088250.

Sequence in context: A004161 A303141 A246070 * A025016 A355499 A094244

Adjacent sequences: A202775 A202776 A202777 * A202779 A202780 A202781

Keyword

more,nonn

Author

Arkadiusz Wesolowski, Jan 06 2012

Extensions

a(14) from Giovanni Resta, Mar 31 2017

Status

approved