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A216389
Number of values of k for which sigma(k) is a permutation of decimal digits of k, for k < 10^n.
0
1, 2, 7, 17, 64, 264, 1106, 5804
OFFSET
1,2
FORMULA
a(n) = # { k in A115920 | k < 10^n }. - M. F. Hasler, Feb 24 2014
EXAMPLE
a(3) = 7 because the values of k satisfying the condition for k < 10^3 are {1, 69, 258, 270, 276, 609, 639}. - V. Raman, Feb 17 2014
MATHEMATICA
With[{ds=Table[If[Sort[IntegerDigits[DivisorSigma[1, n]]]==Sort[ IntegerDigits[ n]], 1, 0], {n, 10^8}]}, Table[Total[Take[ds, 10^i]], {i, 8}]] (* Harvey P. Dale, Apr 20 2017 *)
PROG
(PARI) a(n)=sum(k=1, 10^n, vecsort(digits(k)) == vecsort(digits(sigma(k)))) \\ V. Raman, Feb 17 2014, based on edits by M. F. Hasler
CROSSREFS
Sequence in context: A133407 A182667 A067602 * A154298 A225806 A283754
KEYWORD
nonn,base,more
AUTHOR
V. Raman, Sep 06 2012
STATUS
approved