A216385 Number of values of k for which phi(k) is a permutation of decimal digits of k, for k < 10^n.
1, 3, 5, 21, 78, 403, 2069, 11856, 70835, 437164
Offset: 1
Examples
a(3) = 5 because the values of k satisfying the condition for k < 10^3 are {1, 21, 63, 291, 502}. - _V. Raman_, Feb 17 2014
Programs
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PARI
a(n)=sum(k=1, 10^n, vecsort(digits(k)) == vecsort(digits(eulerphi(k)))) \\ Use digits(n)=eval(Vec(Str(n))) in old versions of PARI. - V. Raman, Feb 17 2014, based on edits by M. F. Hasler
Formula
a(n) = # { k in A115921 | k < 10^n }. - M. F. Hasler, Feb 24 2014
Extensions
a(9) from Jinyuan Wang, Mar 03 2020
a(10) from Amiram Eldar, Nov 30 2024