cp's OEIS Frontend

A115921 Numbers k such that the decimal digits of phi(k) are a permutation of those of k.

%I A115921 #24 Jul 15 2021 21:25:56
%S A115921 1,21,63,291,502,2518,2817,2991,4435,5229,5367,5637,6102,6174,6543,
%T A115921 6822,7236,7422,8022,8541,8982,17631,18231,18261,20301,20518,20617,
%U A115921 21058,22471,22851,25196,25918,27615,29817,34816,35683,43218,44305
%N A115921 Numbers k such that the decimal digits of phi(k) are a permutation of those of k.
%C A115921 Contains A069215 and A113781; is itself a subsequence of A082060. - _M. F. Hasler_, Nov 28 2007
%C A115921 There is some m > 1 such that a(n) > m*n for all n > 1. This follows from the positive density of numbers n such that n/phi(n) > 10. - _Charles R Greathouse IV_, Sep 07 2012
%H A115921 V. Raman, <a href="/A115921/b115921.txt">Table of n, a(n) for n = 1..10000</a>
%e A115921 phi(20301) = 13200, phi(6543) = 4356.
%t A115921 Select[Range[45000],Sort[IntegerDigits[EulerPhi[#]]]==Sort[IntegerDigits[#]]&] (* _Harvey P. Dale_, Jul 25 2018 *)
%o A115921 (PARI) for(n=1,10^5,if(vecsort(Vecsmall(Str(n)))==vecsort(Vecsmall(Str(eulerphi(n)))),print1(n", "))) \\ _M. F. Hasler_, Nov 28 2007
%o A115921 (Python)
%o A115921 from sympy import totient
%o A115921 A115921_list = [n for n in range(1,10**4) if sorted(str(totient(n))) == sorted(str(n))] # _Chai Wah Wu_, Dec 13 2015
%Y A115921 Cf. A069215, A113781, A082060, A115920, A114065, A175795.
%K A115921 nonn,base
%O A115921 1,2
%A A115921 _Giovanni Resta_, Feb 06 2006
%E A115921 Edited by _M. F. Hasler_, Nov 28 2007