A098920 Least k such that k*M#(n) + 1 is prime where M#(n) is the product of the first n Mersenne primes = Product_{j=1..n} A000668(j).

2, 2, 2, 6, 30, 10, 4, 26, 12, 10, 12, 436, 644, 424, 2164, 862, 408, 9558, 5226, 12350

Offset

1,1

Links

Table of n, a(n) for n=1..20.

Example

2*(2^2-1)*(2^3-1)*(2^5-1) + 1 = 1303 prime so a(3)=2.

Mathematica

With[{s = FoldList[Times, Array[2^MersennePrimeExponent@ # - 1 &, 16]]}, Array[Block[{k = 2}, While[! PrimeQ[k s[[#]] + 1], k++]; k] &, Length@ s]] (* Michael De Vlieger, Dec 27 2019 *)

Crossrefs

Sequence in context: A321741 A101416 A371919 * A270557 A129365 A125838

Adjacent sequences: A098917 A098918 A098919 * A098921 A098922 A098923

Keyword

hard,more,nonn

Author

Pierre CAMI, Oct 17 2004

Extensions

a(15)-a(20) from Donovan Johnson, Mar 23 2008

Status

approved