A065015 Sum divides product: number of integer solutions (w,x,y,z), w >= x >= y >= z > 0, to the equation w*x*y*z = n*(w+x+y+z).
1, 5, 4, 8, 6, 14, 7, 15, 12, 22, 7, 26, 9, 24, 23, 30, 8, 42, 11, 31, 21, 29, 12, 56, 18, 32, 27, 48, 13, 68, 11, 42, 35, 40, 32, 65, 9, 35, 30, 76, 9, 87, 18, 51, 49, 39, 18, 97, 27, 70, 31, 52, 14, 108, 36, 72, 33, 52, 17, 120, 15, 37, 66, 90, 36, 93, 12, 63, 44, 123, 19, 130
Offset: 1
Keywords
Examples
a(7) = 7, since there are seven such solutions to wxyz = 7(w+x+y+z): (42,2,2,2), (49,4,2,1), (7,4,4,1), (10,7,2,1), (70,8,1,1), (28,10,1,1) and (16,14,1,1).
Programs
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PARI
A065015(n,d=0)={sum(x=1,sqrtn(4*n+.5,3),sum(y=x,sqrtint(4*n\x),sum(z=max(y,n\(x*y)+1),4*n\(x*y),(x+y+z)*n%(x*y*z-n)==0&&(x+y+z)*n>=(x*y*z-n)*z&&!(d&&print1([x,y,z,t=(x+y+z)*n/(x*y*z-n),x*y*z*t/(x+y+z+t)])))))} \\ M. F. Hasler, Aug 01 2015
Comments