OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
24871 is in the sequence because the prime distinct divisors are {7, 11, 17, 19} and 19^2 + 7^2 = 11^2 + 17^2 = 410.
Although the early terms are all odd with four distinct prime factors, 7212590 = 2 * 5 * 7 * 11 * 17 * 19 * 29 has seven distinct prime factors, and 2^2 + 29^2 = 5^2 + 7^2 + 11^2 + 17^2 + 19^2 = 845. - D. S. McNeil, Nov 12 2011
MAPLE
isA199857 := proc(n)
local p;
p := sort(convert((numtheory[factorset](n)), list)) ;
if nops(p) >= 3 then
return ( op(1, p)^2 + op(-1, p)^2 = add(op(i, p)^2, i=2..nops(p)-1) ) ;
else
false;
end if;
end proc:
for n from 2 to 1500000 do
if isA199857(n) then
printf("%d, ", n) ;
end if ;
end do: # program from R. J. Mathar adapted for this sequence - see A199745
MATHEMATICA
Select[Range[1400000], Plus@@((pl=First/@FactorInteger[#])^2/2) == pl[[1]]^2+pl[[-1]]^2&] (* program from Ray Chandler adapted for this sequence - see A199745 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Nov 11 2011
STATUS
approved