Smallest k > n such that there are exactly n pairs (x,y) (1 <= x <= y <= k) solutions of the equation: phi(xy)=sigma(x)+sigma(y).
A071780
Smallest k > n such that there are exactly n pairs (x,y) (1 <= x <= y <= k) solutions of the equation: phi(xy)=sigma(x)+sigma(y).
Terms
- a(0) =1a(1) =7a(2) =12a(3) =15a(4) =21a(5) =26a(6) =30a(7) =33a(8) =38a(9) =60a(10) =63a(11) =65a(12) =120a(13) =189a(14) =240a(15) =296a(16) =344a(17) =442a(18) =480a(19) =567a(20) =960a(21) =1476a(22) =1701a(23) =1920a(24) =3840a(25) =4448a(26) =5103a(27) =7680a(28) =15309a(29) =15360
External references
- oeis: A071780