A209188 Smallest prime factor of n^2 + n - 1.

5, 11, 19, 29, 41, 5, 71, 89, 109, 131, 5, 181, 11, 239, 271, 5, 11, 379, 419, 461, 5, 19, 599, 11, 701, 5, 811, 11, 929, 991, 5, 19, 29, 1259, 11, 5, 1481, 1559, 11, 1721, 5, 31, 1979, 2069, 2161, 5, 2351, 31, 2549

Offset

2,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 2..1000

PrimeFan, Listing of Esoteric Integer Sequences

Mathematica

SPF[n_] := (FactorInteger[n])[[1]][[1]]; Flatten[Table[SPF[n^2 + (n - 1)], {n, 2, 50}]]
Table[FactorInteger[n^2+n-1][[1, 1]], {n, 2, 50}] (* Harvey P. Dale, Aug 20 2014 *)

Prog

(Magma) [Min(PrimeFactors(n^2+n-1)):n in[2..70]]; // Vincenzo Librandi, Sep 18 2016
(PARI) a(n) = vecmin(factor(n^2+n-1)[, 1]); \\ Michel Marcus, Sep 18 2016

Crossrefs

Cf. A071182.

Sequence in context: A130828 A244241 A108151 * A356247 A215886 A088059

Adjacent sequences: A209185 A209186 A209187 * A209189 A209190 A209191

Keyword

nonn

Author

N. J. A. Sloane, Mar 05 2012

Status

approved