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, 34635, 213302

Offset: 1

Author

V. Raman, Sep 06 2012

Keywords

• nonn
• base
• more

Examples

			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
		

Crossrefs

Cf. A115920, A000203.

Programs

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 *)

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

Formula

a(n) = # { k in A115920 | k < 10^n }. - M. F. Hasler, Feb 24 2014

Extensions

a(9)-a(10) from Amiram Eldar, Dec 27 2024