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 A364834 #61 Aug 17 2023 11:06:22
%S A364834 0,2,2,6,11,17,17,25,25,35,35,47,47,61,76,92,92,110,110,130,130,152,
%T A364834 152,176,201,227,227,255,255,285,285,317,317,351,386,422,422,460,460,
%U A364834 500,500,542,542,586,631,677,677,725,725,775,775,827,827,881,936
%N A364834 Sum of positive integers <= n which are multiples of 2 or 5.
%C A364834 a(n) is odd iff 5 <= n mod 20 <= 14. - _Saish S. Kambali_, Aug 14 2023
%H A364834 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,0,2,-2,0,0,0,0,0,0,0,0,-1,1).
%F A364834 a(n) = sn(n,2) + sn(n,5) - sn(n,10) where sn(n,d) = (an(n,d) * (an(n,d) + d))/(2*d) and an(n,d) = d * floor(n/d).
%F A364834 a(n) = Sum_{k=2..n} {k if gcd(k,10) > 1}.
%t A364834 Accumulate[Table[n * Boole[MemberQ[Mod[n, {2, 5}], 0]], {n, 0, 55}]] (* _Amiram Eldar_, Aug 09 2023 *)
%o A364834 (Python)
%o A364834 sn = lambda k, n: ((n // k)*((n // k) + 1) * k) // 2
%o A364834 a = lambda n: sn(2, n) + sn(5, n) - sn(10, n)
%o A364834 print([a(n) for n in range(1, 56)])
%o A364834 (PARI) a(n) = vecsum(select(x->(!(x%2) || !(x%5)), [1..n])); \\ _Michel Marcus_, Aug 09 2023
%Y A364834 Cf. A065502, A126592.
%K A364834 nonn,easy
%O A364834 1,2
%A A364834 _Darío Clavijo_, Aug 09 2023