A219761 - OEIS

A219761

a(1) = 1; for n>1, a(n) = smallest integer > a(n-1) such that a(n)*a(n-i)+1 is prime for all 0 <= i <= n-1.

1, 2, 6, 156, 4260, 117306, 160650, 13937550, 32742516, 3306719796, 7746764190

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OFFSET

1,2

REFERENCES

Rainer Rosenthal, Posting to Sequence Fans Mailing List, Nov 30 2012.

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

After a(1)=1, a(2)=2, a(3)=6, we want the smallest m>6 such that 1+m, 1+2m, 1+6m and 1+m^2 are all prime: this is m = 156 = a(4).

MATHEMATICA

f[a_List] := Block[{m = a, k = a[[-1]] + 6}, While[ Union@ PrimeQ[k*Join[m, {k}] + 1] != {True}, k += 6]; k]; s = {1, 2, 6}; Do[ Print[{n, a = f[s]}]; s = Append[s, a], {n, 4, 9}] (* Robert G. Wilson v, Dec 03 2012 *)

CROSSREFS

Cf. A034881, A081942, A093483.

Sequence in context: A122570 A088430 A246958 * A051240 A003189 A323841

Adjacent sequences: A219758 A219759 A219760 * A219762 A219763 A219764

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane, Dec 01 2012

EXTENSIONS

a(8) and a(9) from Robert G. Wilson v, Dec 03 2012

a(10) and a(11) from Robert G. Wilson v, Dec 04 2012

STATUS

approved