A051956 - OEIS

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A051956

a(n) = smallest number > a(n-1) such that a(1)*a(2)*...*a(n) + 1 and a(1)*a(2)*...*a(n) - 1 are primes.

4, 15, 17, 19, 29, 57, 77, 285, 318, 354, 379, 405, 520, 521, 595, 625, 938, 1706, 1738, 2085, 2345, 2817, 4319, 4529, 7005, 8207, 8232, 9451, 9839, 11044, 11170, 12386, 12421, 12722, 14153, 15220, 15371, 17052, 17965, 18279, 18811, 19890, 21628, 22667, 22746

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..184

MATHEMATICA

a[1] = 4; a[n_] := a[n] = For[k = a[n-1]+1, True, k++, p = Times @@ Array[a, n-1]; If[PrimeQ[k*p+1] && PrimeQ[k*p-1], Print[k]; Return[k]]]; Array[a, 45] (* Jean-François Alcover, Oct 23 2016 *)

PROG

(PARI) lista(nn) = {my (v = vector(nn)); for (n = 1, nn, if (n == 1, p = 1; k = 0; , p = prod(j=1, n-1, v[j]); k = v[n-1]+1); while (! isprime(p*k+1) || ! isprime(p*k-1), k++); v[n] = k; print1(k, ", "); ); } \\ Michel Marcus, Sep 28 2013

CROSSREFS

Cf. A051935, A051957.

Sequence in context: A103540 A065159 A240265 * A308983 A032826 A190709

Adjacent sequences: A051953 A051954 A051955 * A051957 A051958 A051959

KEYWORD

nice,nonn

AUTHOR

Felice Russo, Dec 21 1999

EXTENSIONS

More terms from Michel Marcus, Sep 28 2013

STATUS

approved