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 A018249 #22 Jul 11 2025 08:52:54 %S A018249 1,2,6,18,52,130,310,718,1618,3670,8160,17862,38872,84016,180502, %T A018249 386092,821640,1742536,3681130,7754076,16290046,34136028,71378568, %U A018249 148948138,310248240,645155196,1339484196,2777105128,5750079046,11891268400,24563311308,50685770166,104484802056 %N A018249 a(n) = prime(2^n)-1. %H A018249 Amiram Eldar, <a href="/A018249/b018249.txt">Table of n, a(n) for n = 0..78</a> %H A018249 Paul Cooijmans, <a href="http://web.archive.org/web/20050302171708/http://members.chello.nl/p.cooijmans/gliaweb/tests/num.html">Numbers</a>, Item 18, 1995. %H A018249 Paul Cooijmans, <a href="http://web.archive.org/web/20031006141136/http://members.chello.nl/p.cooijmans/gliaweb/tests/tfg/tfgshort.html">Short Test For Genius</a>, Item 29, 2002. %F A018249 a(n) = A033844(n) - 1. %F A018249 a(n) = A051440(n) - 2. - _Amiram Eldar_, Jul 11 2025 %t A018249 Prime[2^Range[0,30]]-1 (* _Harvey P. Dale_, Sep 30 2016 *) %o A018249 (PARI) a(n) = prime(2^n) - 1; \\ _Amiram Eldar_, Jul 11 2025 %Y A018249 Cf. A000040, A033844, A051438, A051440, A051439. %K A018249 nonn %O A018249 0,2 %A A018249 _N. J. A. Sloane_ %E A018249 More terms from _Amiram Eldar_, Jul 11 2025