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A124865
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Numbers of the form p^2-q^2 with p > q prime.
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6
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5, 16, 21, 24, 40, 45, 48, 72, 96, 112, 117, 120, 144, 160, 165, 168, 192, 240, 264, 280, 285, 288, 312, 336, 352, 357, 360, 408, 432, 480, 504, 520, 525, 528, 552, 600, 648, 672, 720, 768, 792, 816, 832, 837, 840, 888, 912, 936, 952, 957, 960, 1008, 1032, 1080
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OFFSET
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1,1
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COMMENTS
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The only prime term is a(1) = 5.
All odd terms are of the form p^2-4.
All even terms are divisible by 8.
Numbers of the form (p^2-q^2)/8 (p, q odd primes, p>q) are listed in A124866.
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LINKS
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FORMULA
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MATHEMATICA
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With[{nn=60}, Take[Union[#[[2]]^2-#[[1]]^2&/@Subsets[Prime[Range[nn]], {2}]], nn]] (* Harvey P. Dale, Aug 21 2015 *)
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PROG
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(PARI) is(n)=if(n%24, isprimepower(n+4)==2 || isprimepower(n+9)==2, fordiv(n/4, d, if(isprime(n/d/4+d) && isprime(n/d/4-d), return(1))); 0) \\ Charles R Greathouse IV, Feb 17 2014
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CROSSREFS
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Apart from a(1), a subsequence of A177713.
Cf. A045636 (numbers of the form p^2+q^2, p, q primes).
Cf. A124866 (numbers of the form (p^2-q^2)/8, p, q odd primes, p>q).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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