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
Keywords
Links
- Vincenzo Librandi, Table of n, a(n) for n = 2..1000
- PrimeFan, Listing of Esoteric Integer Sequences
- PrimeFan, Esoteric Integer Sequences [Cached copy]
Crossrefs
Cf. A071182.
Programs
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Magma
[Min(PrimeFactors(n^2+n-1)):n in[2..70]];// Vincenzo Librandi, Sep 18 2016
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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 *) -
PARI
a(n) = vecmin(factor(n^2+n-1)[,1]); \\ Michel Marcus, Sep 18 2016