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.
a008847 n = a008847_list !! (n-1) a008847_list = filter ((== 1) . a010052 . a000203 . a000290) [1..] -- Reinhard Zumkeller, Mar 27 2013
with(numtheory): readlib(issqr): for i from 1 to 10^5 do if issqr(sigma(i^2)) then print(i); fi; od;
s = {}; Do[ If[IntegerQ[ Sqrt[ DivisorSigma[1, n^2]]], Print[n]; AppendTo[s, n]], {n, 10^6}]; s (* Jean-François Alcover, May 05 2011 *)
Select[Range[1000000],IntegerQ[Sqrt[DivisorSigma[1,#^2]]]&] (* Harvey P. Dale, Aug 22 2011 *)
is_A008847(n)=issquare(sigma(n^2)) \\ M. F. Hasler, Oct 23 2010
max = 10^11; primes = {5, 7, 11, 13, 17, 19, 23, 31, 41, 43, 47, 83, 89, 191, 193, 239, 307, 443, 463, 499, 557, 701, 743, 1087, 1487, 2309, 3583, 4373, 5087, 5507, 5807, 44179}; subs = Select[ Times @@@ Subsets[primes, 7], # < max &] // Sort; f[e2_, e3_, p_] := If[n = 2^e2*3^e3*p; IntegerQ[ Sqrt[ DivisorSigma[1, n^3]]], Print[{2^e2, 3^e3, p}]; Sow[n]]; r = Reap[ Scan[ ((f[0, 0, #]; f[0, 1, #]; f[0, 3, #]; f[1, 0, #]; f[1, 1, #]; f[1, 3, #]; f[3, 0, #]; f[3, 1, #]; f[3, 3, #])& ), subs]][[2, 1]]; Select[r, # < max &] // Union (* Jean-François Alcover, Sep 07 2012, after Donovan Johnson *)
is(n)=issquare(sigma(n^3)) \\ Charles R Greathouse IV, Jun 20 2013
from functools import reduce from operator import mul from sympy import factorint, integer_nthroot A008849_list, n = [], 1 while n < 10**7: fs = factorint(n) if integer_nthroot(reduce(mul,((p**(3*fs[p]+1)-1)//(p-1) for p in fs),1),2)[1]: A008849_list.append(n) n += 1 # Chai Wah Wu, Apr 05 2021
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