A108656 Least a(n)>0 such that a(n-2)*n^2+a(n-1)*n+a(n) is a prime.

2, 3, 2, 3, 2, 7, 2, 3, 2, 11, 4, 5, 2, 1, 2, 5, 10, 1, 2, 3, 2, 3, 2, 1, 2, 5, 4, 17, 6, 13, 4, 1, 2, 5, 8, 11, 10, 3, 2, 9, 2, 11, 6, 3, 4, 15, 6, 1, 6, 1, 4, 5, 2, 11, 4, 1, 10, 3, 36, 7, 16, 1, 10, 15, 12, 5, 14, 5, 4, 1, 14, 5, 40, 1, 2, 11, 8, 11, 24, 17, 2, 1, 12, 5, 8, 23, 10, 29, 8, 1, 4, 5

Offset

1,1

Comments

Corresponding primes in A108657.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

a(1)=2, a(2)=3 and a(3)=2 because 2*3^2+3*3+2=29 is aprime; a(4)=3, a(5)=2 and a(6)=7 because 3*6^2+2*6+7=127 is a prime.

Mathematica

a=2; b=3; s={a, b}; Do[c=Prime[PrimePi[a*n^2+b*n]+1]-a*n^2-b*n; AppendTo[s, c]; a=b; b=c, {n, 3, 200}]; A108656=s
nxt[{n_, a_, b_}]:=Module[{c=a(n+1)^2+b(n+1)}, {n+1, b, NextPrime[c]-c}]; Join[{2}, Transpose[NestList[nxt, {2, 2, 3}, 100]][[3]]] (* Harvey P. Dale, Dec 17 2013 *)

Crossrefs

Cf. A108657.

Sequence in context: A318620 A287748 A260233 * A164962 A251089 A119880

Adjacent sequences: A108653 A108654 A108655 * A108657 A108658 A108659

Keyword

nonn

Author

Zak Seidov, Jun 14 2005

Status

approved