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 A330349 #17 Jul 21 2022 10:43:24 %S A330349 2,13,101,1147,14999,255223,4849781,111546307,3234846359,100280244553, %T A330349 3710369066381,152125131761557,6541380665830919,307444891294237513, %U A330349 16294579238595005981,961380175077106286767 %N A330349 a(n) = A070826(n+1) - 2^(n-1). %C A330349 Conjecture: For each value of n, the power of each prime number in the prime factorization of a(n) is equal to 1. %e A330349 a(4) = 1147 = 31*37. %e A330349 a(10) = A070826(11) - 2^9 = 100280245065 - 512 = 100280244553 = A000040(4129119109). %o A330349 (PARI) a(n) = prod(k=1, n+1, prime(k))/2 - 2^(n-1); \\ _Michel Marcus_, Dec 11 2019 %o A330349 (Python) %o A330349 from sympy import primorial %o A330349 def A330349(n): return (primorial(n+1)>>1)-(1<<n-1) # _Chai Wah Wu_, Jul 21 2022 %Y A330349 Cf. A000040, A070826. %K A330349 nonn %O A330349 1,1 %A A330349 _Ahmad J. Masad_, Dec 11 2019