This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A216389 #27 Dec 27 2024 08:45:36
%S A216389 1,2,7,17,64,264,1106,5804,34635,213302
%N A216389 Number of values of k for which sigma(k) is a permutation of decimal digits of k, for k < 10^n.
%F A216389 a(n) = # { k in A115920 | k < 10^n }. - _M. F. Hasler_, Feb 24 2014
%e A216389 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
%t A216389 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 *)
%o A216389 (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_
%Y A216389 Cf. A115920, A000203.
%K A216389 nonn,base,more
%O A216389 1,2
%A A216389 _V. Raman_, Sep 06 2012
%E A216389 a(9)-a(10) from _Amiram Eldar_, Dec 27 2024