OFFSET
1,1
REFERENCES
Legendre, Théorie des Nombres, 3rd edition, 1830.
LINKS
W. Duke and R. Schulze-Pilot, Representation of integers by positive ternary quadratic forms and equidistribution of lattice points on ellipsoids, Invent. Math. 99(1990), 49-57.
R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172.
EXAMPLE
5 is the sum of five hexagonal numbers; 11 is the sum of six hexagonal numbers; the other 72 primes are the sum of four hexagonal numbers. - T. D. Noe, Apr 20 2006
MATHEMATICA
nn=201; hex=Table[n(2n-1), {n, 0, nn-1}]; ps=Prime[Range[PrimePi[hex[[ -1]]]]]; Do[n=hex[[i]]+hex[[j]]+hex[[k]]; If[n<=hex[[ -1]]&&PrimeQ[n], ps=DeleteCases[ps, n]], {i, nn}, {j, i, nn}, {k, j, nn}]; ps (* T. D. Noe, Apr 20 2006 *)
CROSSREFS
KEYWORD
easy,fini,nonn
AUTHOR
Jonathan Vos Post, Apr 18 2006
EXTENSIONS
More terms from T. D. Noe, who conjectures that the list shown here is complete. His search up to 7*10^7 gave no further terms. - Apr 20 2006
STATUS
approved