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A216394 Number of values of k for which phi(k) is a permutation of decimal digits of k, for 2^(n-1) < k < 2^n. 2
1, 0, 0, 0, 1, 1, 0, 0, 2, 0, 0, 3, 11, 2, 13, 21, 26, 49, 91, 186, 108, 335, 937, 500, 1681, 4208, 4156 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,9

LINKS

Table of n, a(n) for n=1..27.

FORMULA

a(n) = # { k in A115921 | 2^(n-1) < k < 2^n }. - M. F. Hasler, Feb 24 2014

EXAMPLE

a(14) = 2 because the values of k satisfying the condition for 2^13 < k < 2^14 are {8541, 8982}. - V. Raman, Feb 18 2014

PROG

(PARI) a(n)=sum(k=2^(n-1), 2^n, vecsort(digits(k)) == vecsort(digits(eulerphi(k)))) \\ V. Raman, Feb 18 2014, based on edits by M. F. Hasler

(Python)

from sympy import totient

def A216394(n):

....if n == 1:

........return 1

....c = 0

....for i in range(2**(n-1)+1, 2**n):

........s1, s2 = sorted(str(i)), sorted(str(totient(i)))

........if len(s1) == len(s2) and s1 == s2:

............c += 1

....return c # Chai Wah Wu, Jul 23 2015

CROSSREFS

Cf. A115921, A000010.

Sequence in context: A244120 A277536 A269159 * A028590 A074644 A321256

Adjacent sequences:  A216391 A216392 A216393 * A216395 A216396 A216397

KEYWORD

nonn,base,more

AUTHOR

V. Raman, Sep 06 2012

STATUS

approved

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Last modified September 17 06:52 EDT 2019. Contains 327119 sequences. (Running on oeis4.)