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 A117543 #19 Feb 16 2025 08:33:00 %S A117543 1,4,0,7,6,0,4,3,4,3,4,9,0,2,3,3,8,8,2,2,2,7,5,0,9,2,5,4,1,3,8,7,7,2, %T A117543 5,3,7,7,4,9,1,9,2,7,6,0,0,4,8,8,0,2,6,3,9,2,4,1,4,8,9,7,6,8,0,7,8,9, %U A117543 3,8,0,2,8,0,9,7,6,0,3,5,3,8,6,9,6,3,5,0,4,4,3,4,8,6,1,3,1,3,8,2,5,7 %N A117543 Decimal expansion of the sum of the reciprocals of squared semiprimes. %C A117543 Geoffrey Landis and Jonathan Vos Post (personal communication) show that this constant equals ((P2)^2 + P4)/2, where P2 and P4 are constants in A085548 and A085964, respectively. %H A117543 Richard J. Mathar, <a href="http://arxiv.org/abs/0803.0900">Series of Reciprocal Powers of k-almost Primes</a>, arXiv:0803.0900 [math.NT], 2008-2009. See Table 4. %H A117543 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PrimeZetaFunction.html">Prime Zeta Function</a>. %e A117543 0.14076043434902338822275... = 1/4^2 + 1/6^2 + 1/9^2 + 1/10^2 + 1/14^2 +1/15^2 +... %t A117543 RealDigits[(PrimeZetaP[2]^2 + PrimeZetaP[4])/2, 10, 120][[1]] (* _Amiram Eldar_, Jun 25 2023 *) %Y A117543 Cf. A001358 (semiprimes), A154928 (derivative). %Y A117543 Cf. A131653 (squared triprimes). [_T. D. Noe_, Oct 09 2008] %K A117543 cons,nonn %O A117543 0,2 %A A117543 _T. D. Noe_, Mar 28 2006