cp's OEIS Frontend

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.

A182292 Smallest odd number k such that is equal to the sum of its proper divisors greater than k^(1/n), or 0 if none exist.

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%I A182292 #27 Mar 01 2024 02:07:12
%S A182292 34155,407715,8415
%N A182292 Smallest odd number k such that is equal to the sum of its proper divisors greater than k^(1/n), or 0 if none exist.
%C A182292 a(8) = 159030135. There is no n > 4 for which a(n) is smaller unless a(n) = 0. - _Charles R Greathouse IV_, Apr 25 2012
%C A182292 Other than a(2) to a(4) and a(8), there is no solution < 2*10^10 for a(n) up to a(1000). - _Donovan Johnson_, Aug 23 2012
%C A182292 From _Alexander Violette_, Feb 29 2024: (Start)
%C A182292 a(7) <= 7650499534755.
%C A182292 a(14) <= 221753170660847595. (End)
%e A182292 The sum proper divisors of 407715 greater than 407715^(1/3) is 77 + 105 + 165 + 231 + 353 + 385 + 1059 + 1155 + 1765 + 2471 + 3883 + 5295 + 7413 + 11649 + 12355 + 19415 + 27181 + 37065 + 58245 + 81543 + 135905 = 407715.
%t A182292 t={}; d[n_]:= Select[Drop[Divisors[n],-1], #1>n^(1/p)&]; Do[s=Select[Range[1,5*10^5,2], #==Plus@@d[#]&];
%t A182292   AppendTo[t,s], {p,2,4}]; Flatten[t]
%o A182292 (PARI) a(n)=my(t,k=8413);while(k+=2,if(sigma(k,-1)>2,if(ispower(k,n,&t),,t=k^(1/n)\1);if(sumdiv(k,d,if(d>t,d))==2*k,return(k)))) \\ _Charles R Greathouse IV_, Apr 25 2012
%Y A182292 See A182147 for more details for 34155.
%Y A182292 Cf. A182311, A182286, A005231.
%K A182292 nonn,bref
%O A182292 2,1
%A A182292 _Manuel Valdivia_, Apr 24 2012