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A216395
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Number of values of k for which sigma(k) is a permutation of decimal digits of k, for 2^(n-1) < k < 2^n.
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1
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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
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OFFSET
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1,9
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LINKS
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FORMULA
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EXAMPLE
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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
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PROG
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(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
....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
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CROSSREFS
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KEYWORD
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nonn,base,more
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AUTHOR
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STATUS
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approved
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