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A215816
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Odd numbers n such that the Lucas number L(n) can be written in the form a^2 + 3*b^2.
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4
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1, 3, 9, 11, 17, 19, 27, 33, 41, 43, 51, 57, 67, 73, 81, 83, 99, 113, 121, 123, 129, 139, 153, 171, 201, 219, 241, 243, 249, 281, 283, 297, 313, 323, 339, 353, 363, 369, 379, 387, 401, 417, 443, 457, 459, 473, 513, 569, 571, 577, 603, 617, 657, 723, 729, 747, 843, 849, 857, 881, 891, 939, 969, 1009
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OFFSET
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1,2
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COMMENTS
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These Lucas numbers L(n) have no prime factor congruent to 2 (mod 3) to an odd power.
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LINKS
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MATHEMATICA
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Select[Range[1, 200, 2], Length[FindInstance[x^2 + 3*y^2 == LucasL[#], {x, y}, Integers]] > 0 &] (* T. D. Noe, Aug 27 2012 *)
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PROG
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(PARI) for(i=2, 500, a=factorint(fibonacci(i-1)+fibonacci(i+1))~; has=0; for(j=1, #a, if(a[1, j]%3==2&&a[2, j]%2==1, has=1; break)); if(has==0&&i%2==1, print(i", ")))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Added 32 more terms - V. Raman, Aug 28 2012
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STATUS
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approved
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