A247080 Numbers whose Euler totient is the reverse of the sum of its aliquot parts.
2, 735, 7665, 11505, 42630, 64578, 3440409, 11263073973
Offset: 1
Examples
phi(2) = 1 and sigma(2) - 2 = 1. phi(735) = 336 and sigma(735) - 735 = 633. phi(7665) = 3456 and sigma(7665) - 7665 = 6543.
Programs
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Maple
with(numtheory): T:=proc(w) local x,y,z; x:=w; y:=0; for z from 1 to ilog10(x)+1 do y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end: P:=proc(q) local n; for n from 1 to q do if phi(n)=T(sigma(n)-n) then print(n); fi; od; end: P(10^9);
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Mathematica
Select[Range[10^6], EulerPhi[#] == FromDigits[Reverse[IntegerDigits[DivisorSigma[1, #] - #]]] &] (* Michael De Vlieger, Jan 29 2015 *)
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PARI
rev(n) = subst(Polrev(digits(n)), x, 10); isok(n) = rev(sigma(n)-n) == eulerphi(n); \\ Michel Marcus, Jan 29 2015
Extensions
a(7)-a(8) from Hiroaki Yamanouchi, Nov 22 2014
Comments