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 A287055 Numbers n such that uphi(n) = uphi(n+1), where uphi(n) is the unitary totient function (A047994). 7

%I

%S 1,20,35,143,194,208,740,1119,1220,1299,1419,1803,1892,2232,2623,3705,

%T 3716,3843,4995,5031,5183,5186,5635,7868,10659,17948,18507,18914,

%U 21007,23616,25388,25545,30380,30744,31599,32304,34595,37820,38024,47067,60767,70394

%N Numbers n such that uphi(n) = uphi(n+1), where uphi(n) is the unitary totient function (A047994).

%C The unitary version of A001274 (phi(n) = phi(n+1)). The first terms that are common to both sequences are: 1, 194, 3705, 5186, 25545, 388245, 1659585, 2200694, 2521694, 2619705, 3289934, 4002405, 5781434, 6245546, 6372794, 8338394.

%H Amiram Eldar, <a href="/A287055/b287055.txt">Table of n, a(n) for n = 1..207</a>

%e uphi(20) = uphi(21) = 12, thus 20 is in the sequence.

%t uphi[n_] := If[n==1,1,(Times @@ (Table[#[[1]]^#[[2]] - 1, {1}] & /@ FactorInteger[n]))[[1]]]; a={}; u1=0; For[k=0, k<10^5, k++; u2=uphi[k]; If[u1==u2, a = AppendTo[a, k-1]]; u1=u2]; a

%o (PARI) uphi(n) = my(f = factor(n)); prod(i=1, #f~, f[i,1]^f[i,2]-1);

%o isok(n) = uphi(n+1) == uphi(n); \\ _Michel Marcus_, May 20 2017

%Y Cf. A001274, A047994.

%K nonn

%O 1,2

%A _Amiram Eldar_, May 18 2017

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Last modified September 22 22:24 EDT 2020. Contains 337291 sequences. (Running on oeis4.)