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 A156778 #8 Feb 03 2025 09:48:46 %S A156778 0,1,5,15,34,70,123,203,308,450,645,880,1182,1547,1967,2460,3048,3740, %T A156778 4509,5396,6390,7476,8701,10051,11556,13250,15093,17064,19194,21460, %U A156778 23895,26660,29616,32802,36159,39830,43686,47804,52193,56823,61740 %N A156778 a(n) = n*A007504(n)/2 = n*(sum of first n primes)/2. %C A156778 For n>0, the sum of the first n primes, A007504(n), has the opposite parity of n (since both increase by an odd amount, and A007504(n)=2 for n=1). %F A156778 a(n) = A156780(prime(n))/2, where prime(n) = A000040(n) is the n-th prime. %o A156778 (PARI) vector(80,n,n--;sum(i=1,n,prime(i))*n)/2 %o A156778 (PARI) a(n) = n*vecsum(primes(n))/2 \\ _Jason Yuen_, Feb 03 2025 %Y A156778 Cf. A007504, A156780. %K A156778 nonn %O A156778 0,3 %A A156778 _M. F. Hasler_, Feb 21 2009