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A267434
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Numbers of the form x^2 + x + x*y + y + y^2 (A267137) that are not of the form a^2 + b^2 + c^2 where x, y, a, b and c are integers.
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0
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60, 92, 112, 124, 156, 220, 240, 252, 284, 316, 380, 412, 444, 476, 496, 508, 540, 604, 624, 732, 752, 764, 796, 880, 892, 956, 960, 1008, 1020, 1084, 1136, 1180, 1212, 1244, 1264, 1276, 1308, 1340, 1392, 1436, 1472, 1500, 1520, 1532, 1564, 1596, 1692, 1724, 1776, 1792, 1820, 1852, 1884, 1916, 1980, 1984
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OFFSET
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1,1
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COMMENTS
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Inspiration was the equation x^2 + x + x*y + y + y^2 = a^2 + b^2 + c^2 where x, y, a, b and c are integers.
Complement of this sequence is 0, 1, 2, 4, 5, 6, 8, 9, 10, 12, 14, 16, 17, 20, 21, 22, 24, 25, 26, 30, 32, 33, 34, 36, 37, 40, 41, 42, 44, 46, 49, 50, 52, 54, 56, 57, 58, 64, 65, 66, 69, 70, 72, 74, 76, 80, 81, 82, 85, 86, 89, 90, 94, 96, ...
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LINKS
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EXAMPLE
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60 is a term because 60 = 6^2 + 6 + 6*2 + 2 + 2^2 and there is no integer values of a, b and c for the equation 60 = a^2 + b^2 + c^2.
50 is not a term because 50 = 6^2 + 6 + 6*1 + 1 + 1^2 = 3^2 + 4^2 + 5^2.
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MATHEMATICA
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Select[Range@ 2000, And[Resolve[Exists[{x, y}, Reduce[# == x^2 + x + x y + y + y^2, {x, y}, Integers]]], !Resolve[Exists[{x, y, z}, Reduce[# == x^2 + y^2 + z^2, {x, y, z}, Integers]]]] &] (* Michael De Vlieger, Jan 15 2016 *)
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PROG
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(PARI) isA003136(n) = #bnfisintnorm(bnfinit(z^2+z+1), n);
isA004215(n) = { my(fouri, j) ; fouri=1 ; while( n >=7*fouri, if( n % fouri ==0, j= n/fouri -7 ; if( j % 8 ==0, return(1) ) ; ) ; fouri *= 4 ; ) ; return(0) ; } { for(n=1, 400, if(isA004215(n), print1(n, ", ") ; ) ; ) ; }
for(n=0, 2000, if(isA003136(3*n+1) && isA004215(n), print1(n, ", ")));
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CROSSREFS
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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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