OFFSET
1,2
COMMENTS
All integers of the form p^p*q^q*r^r, with p, q and r primes, are in the sequence.
FORMULA
Solution of the equation n’ = 3*n.
EXAMPLE
337500 = 2^2*3^3*5^5, 337500’ = 1012500 and 337500 = 3*1012500.
MAPLE
with(numtheory): with(combinat): P:=proc(q) local a, k, n, x, y;
x:=[]; y:=[]; for n from 1 to q do for k from 1 to 3 do x:=[op(x), ithprime(n)^ithprime(n)]; od; od;
a:=choose(x, 3); for k from 1 to nops(a) do y:=[op(y), convert(a[k], `*`)]; od; y:=sort([op(y)]); print(0);
for k from 1 to 100 do print(y[k]); od; end: P(10);
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Mar 02 2017
STATUS
approved