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A216395 Number of values of k for which sigma(k) is a permutation of decimal digits of k, for 2^(n-1) < k < 2^n. 1
1, 0, 0, 0, 0, 0, 1, 0, 3, 2, 0, 6, 3, 5, 14, 22, 26, 60, 64, 71, 179, 333, 274, 751, 1653, 1726, 3032 (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 A115920 | 2^(n-1) < k < 2^n }. - M. F. Hasler, Feb 24 2014

EXAMPLE

a(12) = 6 because the values of k satisfying the condition for 2^11 < k < 2^12 are {2391, 2556, 2931, 3409, 3678, 3679}. - V. Raman, Feb 19 2014

PROG

(PARI) a(n)=sum(k=2^(n-1), 2^n, vecsort(digits(k)) == vecsort(digits(sigma(k)))) \\ V. Raman, Feb 19 2014, based on edits by M. F. Hasler

(Python)

from sympy import divisor_sigma

def A216395(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(divisor_sigma(i)))

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

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

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

CROSSREFS

Cf. A115920, A000203.

Sequence in context: A253176 A079408 A114376 * A058096 A049780 A159584

Adjacent sequences:  A216392 A216393 A216394 * A216396 A216397 A216398

KEYWORD

nonn,base,more

AUTHOR

V. Raman, Sep 06 2012

STATUS

approved

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Last modified September 20 07:59 EDT 2019. Contains 327214 sequences. (Running on oeis4.)