A216389
Number of values of k for which sigma(k) is a permutation of decimal digits of k, for k < 10^n.
Original entry on oeis.org
1, 2, 7, 17, 64, 264, 1106, 5804, 34635, 213302
Offset: 1
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
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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 *)
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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
A216390
Number of values of k for which sigma(k) is a permutation of decimal digits of k, for 10^(n-1) < k < 10^n.
Original entry on oeis.org
1, 1, 5, 10, 47, 200, 842, 4698, 28831
Offset: 1
a(3) = 5 because the values of k satisfying the condition for 10^2 < k < 10^3 are {258, 270, 276, 609, 639}. - _V. Raman_, Feb 18 2014
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a(n)=sum(k=10^(n-1), 10^n, vecsort(digits(k)) == vecsort(digits(sigma(k)))) \\ V. Raman, Feb 18 2014, based on edits by M. F. Hasler
A216392
Number of values of k for which sigma(k) is a permutation of decimal digits of k, for k < 2^n.
Original entry on oeis.org
1, 1, 1, 1, 1, 1, 2, 2, 5, 7, 7, 13, 16, 21, 35, 57, 83, 143, 207, 278, 457, 790, 1064, 1815, 3468, 5194, 8226
Offset: 1
a(10) = 7 because the values of k satisfying the condition for k < 2^10 are {1, 69, 258, 270, 276, 609, 639}. - _V. Raman_, Feb 18 2014
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a(n)=sum(k=1, 2^n, vecsort(digits(k)) == vecsort(digits(sigma(k)))) \\ V. Raman, Feb 18 2014, based on edits by M. F. Hasler