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A216396 Number of values of k for which sigma(k)-k is a permutation of decimal digits of k, for 2^(n-1) < k < 2^n. 1
0, 0, 1, 0, 1, 0, 0, 0, 2, 1, 1, 2, 5, 4, 15, 15, 16, 35, 91, 90, 158, 345, 586, 694, 1549, 2700, 3363 (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 A085844 | 2^(n-1) < k < 2^n }. - M. F. Hasler, Feb 24 2014

EXAMPLE

a(13) = 5 because the values of k satisfying the condition for 2^12 < k < 2^13 are {4672, 4896, 5046, 7785, 8128}. - V. Raman, Feb 19 2014

PROG

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

(Python)

from sympy import divisor_sigma

def A216396(n):

....c = 0

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

........s1, s2 = sorted(str(i)), sorted(str(divisor_sigma(i)-i))

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

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

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

CROSSREFS

Cf. A085844, A001065.

Sequence in context: A029937 A289772 A283615 * A273488 A117848 A025242

Adjacent sequences:  A216393 A216394 A216395 * A216397 A216398 A216399

KEYWORD

nonn,base,more

AUTHOR

V. Raman, Sep 06 2012

STATUS

approved

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Last modified October 22 07:29 EDT 2019. Contains 328315 sequences. (Running on oeis4.)