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 A072749 #20 Feb 24 2021 03:50:55 %S A072749 0,0,0,1,1,1,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,6, %T A072749 6,6,6,6,6,7,7,7,7,8,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,10,10,10,10,10,11, %U A072749 11,11,11,12,12,12,12,13,13,13,13,13,13,13,14,14,14,14,14,14,14,14,14,14 %N A072749 Count of factors of 5 in the first n squarefree numbers. %H A072749 Gheorghe Coserea, <a href="/A072749/b072749.txt">Table of n, a(n) for n = 1..10000</a> %F A072749 a(n) ~ n/6. - _Amiram Eldar_, Feb 24 2021 %e A072749 The first 10 squarefree numbers are: 1, 2, 3, 5, 6=2*3, 7, 10=2*5, 11, 13 and 14=2*7: 5 and 10 are divisible by 5, therefore a(10)=2. %t A072749 Accumulate[If[Divisible[#,5],1,0]&/@Select[Range[150],SquareFreeQ]] (* _Harvey P. Dale_, Oct 17 2013 *) %o A072749 (PARI) %o A072749 n = 89; k = 0; bag = List(); a = vector(n); %o A072749 until(n == 0, k++; if (issquarefree(k), listput(bag, k); n--)); %o A072749 for (i=2, #bag, a[i] = a[i-1] + (bag[i] % 5 == 0)); %o A072749 print(a); \\ _Gheorghe Coserea_, Aug 22 2015 %Y A072749 Cf. A005117, A072747, A072748, A072750, A072751. %K A072749 nonn %O A072749 1,7 %A A072749 _Reinhard Zumkeller_, Jul 08 2002 %E A072749 Name clarified by _Gheorghe Coserea_, Aug 22 2015