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A216391 Number of values of k for which phi(k) is a permutation of decimal digits of k, for k < 2^n.

%I A216391 #43 Nov 09 2024 04:38:07
%S A216391 1,1,1,1,2,3,3,3,5,5,5,8,19,21,34,55,81,130,221,407,515,850,1787,2287,
%T A216391 3968,8176,12332,18560,36832,71375,94015,173754
%N A216391 Number of values of k for which phi(k) is a permutation of decimal digits of k, for k < 2^n.
%C A216391 Partial sums of A216394.
%F A216391 a(n) = # { k in A115921 | k < 2^n }. - _M. F. Hasler_, Feb 24 2014
%e A216391 a(12) = 8 because the values of k satisfying the condition for k < 2^12 are {1, 21, 63, 291, 502, 2518, 2817, 2991}. - _V. Raman_, Feb 18 2014
%p A216391 A216391 := proc(n)
%p A216391     local a,k,kdgs,pdgs ;
%p A216391     a := 0 ;
%p A216391     for k from 1 to 2^n do
%p A216391         kdgs := sort(convert(k,base,10)) ;
%p A216391         numtheory[phi](k) ;
%p A216391         pdgs := sort(convert(%,base,10)) ;
%p A216391         if pdgs = kdgs then
%p A216391             a := a+1 ;
%p A216391         end if;
%p A216391     end do:
%p A216391     a ;
%p A216391 end proc:
%p A216391 for n from 1 do
%p A216391     print(A216391(n)) ;
%p A216391 end do: # _R. J. Mathar_, Mar 04 2014
%o A216391 (PARI) a(n)=sum(k=1, 2^n, vecsort(digits(k)) == vecsort(digits(eulerphi(k)))) \\ _V. Raman_, Feb 18 2014, edited by _M. F. Hasler_, Mar 04 2014
%Y A216391 Cf. A000010, A115921, A216394.
%K A216391 nonn,base,more
%O A216391 1,5
%A A216391 _V. Raman_, Sep 06 2012
%E A216391 a(28)-a(32) from _Amiram Eldar_, Nov 09 2024