OFFSET
1,1
COMMENTS
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
EXAMPLE
9 is in the sequence because for (x,y,z) = (1,2,2), x^2 + y^2 + z^2 = 9, phi(4)=2, sigma(4)=7, and phi(4) + sigma(4) = 9 ;
1640 is in the sequence because for (x,y,z) = (6,2,40), x^2 + y^2 + z^2 = 1640, phi(480)=128, sigma(480)=1512, and phi(480) + sigma(480) = 1640.
MAPLE
isA173792 := proc(n)
for x from 1 do
if x^2 > n then
return false;
end if;
for y from x do
if x^2+y^2 > n then
break;
end if;
if issqr(n-x^2-y^2) then
z := sqrt(n-x^2-y^2) ;
p := x*y*z ;
if n = numtheory[sigma](p) + numtheory[phi](p) then
return true;
end if;
end if;
end do:
end do:
end proc:
for n from 1 do
if isA173792(n) then
printf("%d, \n", n) ;
end if;
end do: # R. J. Mathar, Jul 08 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 24 2010
STATUS
approved