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 A139240 #10 Oct 20 2023 16:55:23 %S A139240 1,6,24,480,1536,30720,98304,1966080,132120576,402653184,33822867456, %T A139240 515396075520,1649267441664,32985348833280,2216615441596416, %U A139240 141863388262170624,432345564227567616,36317027395115679744,553402322211286548480,1770887431076116955136,148754544210393824231424 %N A139240 First differences of Mersenne numbers A001348, divided by 4. %H A139240 Paolo Xausa, <a href="/A139240/b139240.txt">Table of n, a(n) for n = 1..450</a> %F A139240 a(n) = A139238(n)/4 = A139239(n)/2. %t A139240 Differences[2^Prime[Range[25]]-1]/4 (* _Paolo Xausa_, Oct 20 2023 *) %o A139240 (PARI) a(n)=my(p=prime(n));(2^nextprime(p+1)-2^p)/4 \\ _Charles R Greathouse IV_, Jan 03 2013 %Y A139240 Cf. A001348, A139237, A139238, A139239, A139243. %K A139240 easy,nonn %O A139240 1,2 %A A139240 _Omar E. Pol_, Apr 19 2008 %E A139240 a(10)-a(21) from _Paolo Xausa_, Oct 20 2023