A094805 Duplicate of A055193.
6, 210, 840, 341880, 71831760, 64648584000, 2216650756320
Offset: 1
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(n)=my(N=1+#n=divisors(2*n));sum(i=1,N\2,issquare(n[i]^2+n[N-i]^2));
a(2) = 210 is the smallest area common to 2 primitive Pythagorean triangles (viz. triples {20, 21, 29}, {12, 35, 37}); followed by 2730 (triples {60, 91, 109}, {28, 195, 197}); 7980 (triples {95, 168, 193}, {40, 399, 401}); 71610 (triples {341, 420, 541}, {132, 1085, 1093}); ...
p^2 - p*q + q^2 = r^2; p = 115, q = 448, q-p = 333, r = 403; k = p*q*(q-p)*r = 115*448*333*403 = 6913932480. x = 414, y = 104 and x = 558, y = 40 gives the same area. k = x*y*(x-y)*(x+y) = 414*104*310*518 = 6913932480. k = x*y*(x-y)*(x+y) = 558*40*518*598 = 6913932480.
p^2 - p*q + q^2 = r^2; p = 208, q = 418, r = 362, q - p = 210; n = p*r*q*(q-p) = 208*418*362*210 = 6609482880. x = 640, y = 627 gives the same area: n = x*y*(x-y)*(x+y) = 640*627*13*1267 = 6609482880.
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