login
phi(n) + phi(reverse(n)) = sigma(n).
0

%I #9 Aug 26 2021 16:46:21

%S 3,26,221,635,1702,4945,5038,26596,27927,62783,195723,210221,364287,

%T 489955,495995,525833,901303,909503,2747761,2750247,2941119,3926146,

%U 4463651,4484831,4630475,4769947,5531305,6099313,6482845,6917881

%N phi(n) + phi(reverse(n)) = sigma(n).

%e phi(221) + phi(reverse(221)) = phi(221) + phi(122) = 192 + 60 = 252 = sigma(221).

%t r = {}; Do[ If[ EulerPhi[n] + EulerPhi[ FromDigits[ Reverse[ IntegerDigits[n]]]] == DivisorSigma[1, n], r = Append[r, n]], {n, 1, 10^7}]; r

%t Select[Range[7*10^6],EulerPhi[#]+EulerPhi[IntegerReverse[#]] == DivisorSigma[ 1,#]&] (* _Harvey P. Dale_, Aug 26 2021 *)

%K base,nonn

%O 1,1

%A _Joseph L. Pe_, Jun 09 2002

%E Edited and extended by _Robert G. Wilson v_, Jun 11 2002

%E Corrected by _Harvey P. Dale_, Aug 26 2021