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 A070308 #40 Feb 27 2024 03:00:05
%S A070308 125,581,8549,16999
%N A070308 "Canada perfect numbers": n such that the sum of digits^2 of n equals the sum of d|n, 1<d<n.
%C A070308 Those numbers were defined by J. Fabrykowski, B. Wolk and R. Padmanabhan (University of Manitoba) for the 125th anniversary of Canada.
%C A070308 There are no further terms. - _David Wasserman_, May 13 2003
%D A070308 J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 125, p. 43, Ellipses, Paris 2008.
%D A070308 Jean-Marie De Koninck and Armel Mercier, Introduction à la théorie des nombres, Collection Universitaire de Mathématiques, Modulo, p. 85.
%D A070308 J.-M. De Koninck and A. Mercier, 1001 Problèmes en Théorie Classique Des Nombres, Problem 700 pp. 91; 299, Ellipses Paris 2004.
%e A070308 125 is a term because 1^2 + 2^2 + 5^2 = 30 = 5 + 25.
%p A070308 select(t -> add(x^2, x=convert(t,base,10)) = numtheory:-sigma(t) - 1 - t, [$1..20000]); # _Robert Israel_, Apr 07 2016
%t A070308 cnQ[n_]:=Module[{sod=Total[Rest[Most[Divisors[n]]]]},sod == Total[IntegerDigits[n]^2]]; Select[Range[2, 17000], cnQ] (* _Harvey P. Dale_, Jun 17 2011 *)
%o A070308 (PARI) isok(n) = my(d=digits(n)); sum(k=1, #d, d[k]^2) == sigma(n) - n - 1; \\ _Michel Marcus_, Apr 07 2016
%K A070308 nonn,base,easy,fini,full
%O A070308 1,1
%A A070308 _Benoit Cloitre_, May 12 2002