OFFSET
0,1
COMMENTS
Bisection of A060395.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..10000
Carlos Rivera, Conjecture 17. The Ludovicus conjecture about the Euler trinomials, The Prime Puzzles & Problems Connection.
FORMULA
a(n)=3 if n is equal to 0 or 1 mod 3.
EXAMPLE
To obtain a(3), note that x^2+x+7 takes the values 7,9,13,19,... for k=0,1,2,... and the smallest prime dividing these numbers is 3.
MATHEMATICA
a[n_] := Switch[n, 0, 3, _, Module[{f, kmax0 = 2}, f[kmax_] := f[kmax] = MinimalBy[Table[{k, FactorInteger[k^2 + k + 2 n + 1][[1, 1]]}, {k, 0, kmax}], Last, 1]; f[kmax = kmax0]; f[kmax = 2 kmax]; While[f[kmax] != f[kmax/2], kmax = 2 kmax]; f[kmax][[1, 2]]]];
Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Aug 15 2022 *)
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
N. J. A. Sloane, Apr 04 2001
EXTENSIONS
More terms from Matthew Conroy, Apr 18 2001
STATUS
approved