A087338 a(1) = 1, then the smallest number > 1 such that both every partial sum and every partial product + 1 are prime for n > 1.

1, 2, 2, 18, 6, 8, 30, 4, 26, 6, 6, 4, 50, 4, 56, 6, 22, 6, 50, 40, 12, 24, 138, 20, 132, 70, 78, 8, 232, 2, 160, 144, 32, 322, 12, 44, 216, 294, 60, 394, 1460, 82, 54, 452, 168, 1024, 86, 76, 308, 208, 104, 456, 268, 396, 350, 120, 10, 236, 180, 402, 112, 336, 530, 318, 112

Offset: 1

Author

Amarnath Murthy, Sep 06 2003

Keywords

• nonn

Examples

			Partial sums: 1+2 = 3, 1+2+2 = 5, 1+2+2+18 = 23;
partial products + 1: 1*2 + 1 = 3, 1*2*2 + 1 = 5, 1*2*2*18 + 1 = 73.
		

Programs

Mathematica

a = {1}; s = 1; p = 1; Do[k = 2; While[ !PrimeQ[s + k] || !PrimeQ[p*k + 1], k++ ]; AppendTo[a, k]; s += k; p *= k, {n, 1, 65}]

Extensions

More terms from Robert G. Wilson v, Sep 07 2003