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A273800
Numbers n for which n = phi(x)*phi(y), where n = x + y and phi(x) is the Euler totient function of x.
2
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
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
Sequence in context: A190037 A110558 A298703 * A273798 A163283 A036705
KEYWORD
nonn
AUTHOR
Paolo P. Lava, May 31 2016
EXTENSIONS
a(19)-a(39) from Giovanni Resta, May 31 2016
STATUS
approved