A216385 - OEIS

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

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..10.

FORMULA

a(n) = # { k in A115921 | k < 10^n }. - M. F. Hasler, Feb 24 2014

EXAMPLE

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

PROG

(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

CROSSREFS

Cf. A115921, A000010.

Sequence in context: A071706 A196418 A189560 * A247680 A179265 A084253

Adjacent sequences: A216382 A216383 A216384 * A216386 A216387 A216388

KEYWORD

nonn,base,more,changed

AUTHOR

V. Raman, Sep 06 2012

EXTENSIONS

a(9) from Jinyuan Wang, Mar 03 2020

a(10) from Amiram Eldar, Nov 30 2024

STATUS

approved