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 A319880 #15 Nov 06 2018 03:00:55
%S A319880 0,1,2,2,10,2,34,-82,46,302,814,-262,1786,-21838,-13646,2738,35506,
%T A319880 -379438,-248366,-9175402,-8651114,-7602538,-5505386,-214704262,
%U A319880 -206315654,-189538438,-155984006,-88875142,45342586,-5932822318,-5395951406,-198413006482
%N A319880 Difference between 2^n and the product of primes less than or equal to n.
%C A319880 This sequence shows 2^n is neither a lower bound nor an upper bound for the primorials.
%F A319880 a(n) = 2^n - n#, where n# is the product of primes less than or equal to n (A034386).
%F A319880 a(n) = A000079(n) - A034386(n) .
%p A319880 restart;
%p A319880 with(NumberTheory);
%p A319880 a := n -> 2^n-product(ithprime(i), i = 1 .. PrimeCounting(n)):
%p A319880 0, seq(a(n), n = 1 .. 15); # _Stefano Spezia_, Nov 05 2018
%t A319880 Table[2^n - Times@@Select[Range[n], PrimeQ], {n, 0, 31}]
%o A319880 (PARI) a(n) = 2^n - prod(k=1, primepi(n), prime(k)); \\ _Michel Marcus_, Nov 05 2018
%Y A319880 Cf. A000079, A054850, A319852, A319857.
%K A319880 sign
%O A319880 0,3
%A A319880 _Alonso del Arte_, Sep 30 2018