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.
a(4) = 8 because A185729(4) = 51 which is the sum of its first 8 non-divisors.
30 is in the sequence because d(1) + d(2) + d(3) + d(4) = 1 + 2 + 3 + 5 = 11 and nd(1) + nd(2) = 4 + 7 = 11.
with(numtheory):nn:=300:
for n from 1 to nn do:
d:=divisors(n):n0:=nops(d):lst:={}:ii:=0:
for i from 1 to n do:
lst:=lst union {i}:
od:
lst:=lst minus d:n1:=nops(lst):
for m from 1 to n0 while(ii=0) do:
s1:=sum(‘d[i]’, ‘i’=1..m):
for j from 1 to n1 while(ii=0) do:
s2:=sum(‘lst[i]’, ‘i’=1..j):
if s1=s2
then
ii:=1:printf(`%d, `,n):
else
fi:
od:
od:
od:
fQ[n_] := Block[{d = Divisors@ n}, nd = nd = Complement[Range@ n, d]; Intersection[Accumulate@ d, Accumulate@ nd] != {}]; Select[ Range@135, fQ] (* Robert G. Wilson v, Mar 06 2018 *)
isok(n) = {d = divisors(n); psd = vector(#d, k, sum(j=1, k, d[j])); nd = setminus([1..n], d); psnd = vector(#nd, k, sum(j=1, k, nd[j])); #setintersect(psd, psnd) != 0;} \\ Michel Marcus, May 05 2018
Comments