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 A068208 #32 Apr 20 2025 02:30:51
%S A068208 4,8,81,441,625,1089,2024,2401,3025,3968,5624,5929,6561,6723,7569,
%T A068208 8281,8463,12321,13225,13688,14161,14641,14884,15375,16641,20164,
%U A068208 21608,24025,25921,26895,28561,34225,46225,55225,55695,61009,62001,67081
%N A068208 Numbers k such that tau(k) - tau(k+1) = 1.
%C A068208 Numbers k such that A000005(k) - A000005(k+1) = 1.
%C A068208 a(n) cannot be a prime.
%C A068208 a(n) or a(n) + 1 is a perfect square as its number of divisors must be odd. - _David A. Corneth_, Dec 26 2020
%H A068208 David A. Corneth, <a href="/A068208/b068208.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Enrique Pérez Herrero)
%t A068208 Select[Range[10^5], DivisorSigma[0, #] - DivisorSigma[0, # + 1] == 1 &] (* _Michael De Vlieger_, Dec 02 2015 *)
%t A068208 Position[Differences[DivisorSigma[0,Range[70000]]],-1]//Flatten (* _Harvey P. Dale_, May 22 2020 *)
%o A068208 (PARI) isok(n) = numdiv(n) - numdiv(n+1) == 1; \\ _Michel Marcus_, Dec 02 2015
%o A068208 (PARI) list(lim) = {my(d, e, k2); for(k = 2, lim, e = factor(k)[, 2]; d = vecprod(apply(x -> 2*x + 1, e)); k2 = k^2; if(numdiv(k2-1) == d+1, print1(k2-1, ", ")); if(numdiv(k2+1) == d-1, print1(k2, ", ")));} \\ _Amiram Eldar_, Apr 20 2025
%Y A068208 Cf. A000005.
%K A068208 nonn,easy
%O A068208 1,1
%A A068208 _Benoit Cloitre_, Mar 23 2002