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 A133049 #8 Oct 03 2017 02:12:13 %S A133049 9,49,961,16129,67092481,17179607041,274876858369,4611686014132420609, %T A133049 5316911983139663487003542222693990401, %U A133049 383123885216472214589586755549637256619304505646776321 %N A133049 Squares of Mersenne primes A000668(n). %C A133049 Sum of last A000043(n) divisors of the n-th even perfect number. In other words; sum of divisors that are not powers of 2 of the n-th even perfect number, or sum of divisors that are multiples of the n-th Mersenne prime A000668(n) of the n-th even perfect number. See A139247 for more information. %C A133049 See the structure of the divisors of perfect numbers in A135652, A135653, A135654 and A135655. %H A133049 G. C. Greubel, <a href="/A133049/b133049.txt">Table of n, a(n) for n = 1..15</a> %H A133049 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %F A133049 a(n) = A000668(n)^2 %e A133049 a(3)=961 because the 3rd Mersenne prime is 31 and 31^2=961. %t A133049 Select[2^Range[1000] - 1, PrimeQ]^2 (* _G. C. Greubel_, Oct 03 2017 *) %o A133049 (PARI) forprime(p=2, 1000, if(ispseudoprime(2^p-1), print1((2^p-1)^2", "))) \\ _G. C. Greubel_, Oct 03 2017 %Y A133049 Cf. A000290, A001248. Mersenne primes: A000668. %Y A133049 Cf. A000043, A000396, A135652, A135653, A135654, A135655, A138247. %K A133049 nonn %O A133049 1,1 %A A133049 _Omar E. Pol_, Oct 30 2007, Apr 23 2008 %E A133049 More terms from _Olaf Voß_, Feb 13 2008