A273800 Numbers n for which n = phi(x)*phi(y), where n = x + y and phi(x) is the Euler totient function of x.

8, 12, 16, 24, 32, 36, 48, 96, 128, 160, 192, 288, 768, 1152, 2048, 2560, 3072, 27648, 110592, 192704, 196608, 202496, 232448, 370688, 379904, 394264, 443512, 466048, 508672, 524288, 553120, 571008, 586016, 607744, 624704, 650624, 655360, 675584, 681856

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..1000

Example

8 = 3+5 = phi(3)*phi(5) = 2*4;
12 = 3+9 = phi(3)*phi(9) = 2*6;
24 = 3+21 = phi(3)*phi(21) = 2*12 or 24 = 10+14 = phi(10)*phi(14) = 4*6.

Maple

with(numtheory): P:=proc(q) local a, b, k, n; for n from 1 to q do
for k from 1 to trunc(n/2) do if phi(k)*phi(n-k)=n then print(n); break; fi;
od; od; end: P(10^9);

Prog

(PARI) is(n)=for(x=1, n\2, if(eulerphi(x)+eulerphi(n-x)==n, return(1))); 0 \\ Charles R Greathouse IV, Jun 07 2016

Crossrefs

Cf. A000010, A273801.

Sequence in context: A190037 A110558 A298703 * A273798 A163283 A036705

Adjacent sequences: A273797 A273798 A273799 * A273801 A273802 A273803

Keyword

nonn

Author

Paolo P. Lava, May 31 2016

Extensions

a(19)-a(39) from Giovanni Resta, May 31 2016

Status

approved