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A108151
a(n) = n^2 + 3*n + 1 if prime or 0 if composite.
0
5, 11, 19, 29, 41, 0, 71, 89, 109, 131, 0, 181, 0, 239, 271, 0, 0, 379, 419, 461, 0, 0, 599, 0, 701, 0, 811, 0, 929, 991, 0, 0, 0, 1259, 0, 0, 1481, 1559, 0, 1721, 0, 0, 1979, 2069, 2161, 0, 2351, 0, 2549, 0
OFFSET
1,1
EXAMPLE
1^2+3*1+1 = 5 prime so a(1) = 5.
2^2+3*2+1 = 11 prime so a(2) = 11.
6^2+3*6+1 = 55 = 5*11 composite so a(6) = 0.
MATHEMATICA
Table[t=n^2+3n+1; If[PrimeQ[t], t, 0], {n, 50}] (* James C. McMahon, Feb 21 2024 *)
CROSSREFS
Cf. A028387.
Sequence in context: A239732 A130828 A244241 * A209188 A356247 A215886
KEYWORD
nonn,less
AUTHOR
Pierre CAMI, Jun 06 2005
STATUS
approved