A070856
Numbers n such that sigma(reverse(n)) = phi(n).
Original entry on oeis.org
1, 120, 260, 450, 861, 1411, 1541, 1550, 7372, 7957, 8393, 9312, 13811, 14840, 20440, 26060, 38323, 41550, 46990, 49813, 51412, 61050, 77695, 78625, 86691, 94604, 94632, 138631, 143520, 166331, 169360, 176820, 182750, 208150, 236220, 236840, 270650
Offset: 1
sigma(reverse(120)) = sigma(21) = 32 = phi(120), so 120 is a term of the sequence.
A252255
Numbers n such that sigma(Rev(phi(n))) = phi(Rev(sigma(n))), where sigma is the sum of divisors and phi the Euler totient function.
Original entry on oeis.org
1, 14, 61, 966, 1428, 9174, 15642, 19934, 22155, 27075, 36650, 48731, 51095, 54184, 57902, 59711, 61039, 89276, 98645, 113080, 126850, 140283, 142149, 154670, 165822, 190908, 197705, 198712, 202096, 203107, 247268, 274368, 274716, 307836, 311925, 331037, 366740
Offset: 1
phi(14) = 6, Rev(6) = 6 and sigma(6) = 12;
sigma(14) = 24, Rev(24) = 42 and sigma(42) = 12.
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with(numtheory): T:=proc(w) local x, y, z; x:=0; y:=w;
for z from 1 to ilog10(w)+1 do x:=10*x+(y mod 10); y:=trunc(y/10); od; x; end:
P:=proc(q) local a, b, k; global n; for n from 1 to q do
if sigma(T(phi(n)))=phi(T(sigma(n))) then print(n); fi; od; end: P(10^12);
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Select[Range[400000],DivisorSigma[1,IntegerReverse[EulerPhi[#]]] == EulerPhi[ IntegerReverse[ DivisorSigma[ 1,#]]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 15 2017 *)
Showing 1-2 of 2 results.