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 A074795 #22 Aug 29 2020 06:00:08 %S A074795 0,0,0,1,1,1,1,1,2,2,2,3,3,3,3,3,3,4,4,5,5,5,5,5,6,6,6,7,7,7,7,8,8,8, %T A074795 8,9,9,9,9,9,9,9,9,10,11,11,11,11,12,13,13,14,14,14,14,14,14,14,14,15, %U A074795 15,15,16,16,16,16,16,17,17,17,17,18,18,18,19,20,20,20,20,20,20,20,20,21 %N A074795 Number of numbers k <= n such that tau(k) == 0 (mod 3) where tau(k) = A000005(k) is the number of divisors of k. %H A074795 Amiram Eldar, <a href="/A074795/b074795.txt">Table of n, a(n) for n = 1..10000</a> %H A074795 L. G. Sathe, <a href="https://www.jstor.org/stable/2371953">On a congruence property of the divisor function</a>, American Journal of Mathematics, Vol. 67, No. 3 (1945), pp. 397-406. %F A074795 a(n) is asymptotic to c*n with c = 0.26.... %F A074795 The constant is c = 1 - zeta(3)/zeta(2) = 1 - 6*zeta(3)/Pi^2 = 0.2692370305 ... (Sathe, 1945). - _Amiram Eldar_, Aug 29 2020 %t A074795 Accumulate[Boole[Divisible[DivisorSigma[0,Range[90]],3]]] (* _Harvey P. Dale_, Jan 11 2015 *) %o A074795 (PARI) a(n)=sum(k=1,n,if(numdiv(k)%3,0,1)) %Y A074795 Cf. A000005, A059269, A074794, A074796. %K A074795 nonn %O A074795 1,9 %A A074795 _Benoit Cloitre_, Sep 07 2002