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A139491
Numbers arising in A139490.
24
3, 8, 9, 12, 15, 16, 21, 24, 40, 45, 48, 60, 72, 120, 168, 240, 840, 1848
OFFSET
1,1
COMMENTS
M. F. Hasler, Apr 24 2008, observed that the numbers in this sequence are differences of two squares. For example: 3=2^2-1^2, 8=3^2-1^2, 9=5^2-4^2, 15=4^2-1^2, 16=5^2-3^2, 21=5^2-2^2, 24=5^2-1^2, 40=7^2-3^2, 45=7^2-2^2, 48=7^2-1^2, 60=8^2-2^2.
This sequence is a subsequence of A024352.
These numbers appear to be a subset of the idoneal numbers A000926. If so, then the sequence is probably complete. - T. D. Noe, Apr 27 2009
LINKS
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
MATHEMATICA
f = 200; g = 300; h = 30; j = 100; b = {}; Do[a = {}; Do[Do[If[PrimeQ[x^2 + n y^2], AppendTo[a, x^2 + n y^2]], {x, 0, g}], {y, 1, g}]; AppendTo[b, Take[Union[a], h]], {n, 1, f}]; Print[b]; c = {}; Do[a = {}; Do[Do[If[PrimeQ[n^2 + w*n*m + m^2], AppendTo[a, n^2 + w*n*m + m^2]], {n, m, g}], {m, 1, g}]; AppendTo[c, Take[Union[a], h]], {w, 1, j}]; Print[c]; bb = {}; cc = {}; Do[Do[If[b[[p]] == c[[q]], AppendTo[bb, p]; AppendTo[cc, q]], {p, 1, f}], {q, 1, j}]; Union[bb]
CROSSREFS
Sequence in context: A047472 A304204 A028960 * A084387 A080761 A087286
KEYWORD
nonn
AUTHOR
Artur Jasinski, Apr 24 2008, Apr 26 2008
EXTENSIONS
Extended by T. D. Noe, Apr 27 2009
STATUS
approved