A216389 Number of values of k for which sigma(k) is a permutation of decimal digits of k, for k < 10^n.

1, 2, 7, 17, 64, 264, 1106, 5804

Offset

1,2

Links

Table of n, a(n) for n=1..8.

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

Cf. A115920, A000203.

Sequence in context: A133407 A182667 A067602 * A154298 A225806 A283754

Adjacent sequences: A216386 A216387 A216388 * A216390 A216391 A216392

Keyword

nonn,base,more

Author

V. Raman, Sep 06 2012

Status

approved