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 A210679 #26 Sep 16 2023 05:28:06
%S A210679 0,1,1,1,1,2,1,1,1,2,0,2,0,2,2,1,0,2,0,2,2,1,0,2,1,1,1,2,0,3,0,1,1,1,
%T A210679 2,2,0,1,1,2,0,3,0,1,2,1,0,2,1,2,1,1,0,2,1,2,1,1,0,3,0,1,2,1,1,2,0,1,
%U A210679 1,3,0,2,0,1,2,1,1,2,0,2,1,1,0,3,1,1
%N A210679 Number of distinct prime factors <= 7 of n.
%C A210679 Periodic with period length 210. - _Amiram Eldar_, Sep 16 2023
%H A210679 Reinhard Zumkeller, <a href="/A210679/b210679.txt">Table of n, a(n) for n = 1..10000</a>
%H A210679 <a href="/index/Rec#order_14">Index entries for linear recurrences with constant coefficients</a>, signature (-3,-5,-6,-6,-5,-3,0,3,5,6,6,5,3,1).
%F A210679 a(n) <= 4.
%F A210679 a(A008364(n)) = 0; a(A080672(n)) > 0.
%F A210679 a(n) = A001221(n) iff n is 7-smooth: a(A002473(n)) = A001221(A002473(n)). [corrected by _Amiram Eldar_, Sep 16 2023]
%F A210679 From _Amiram Eldar_, Sep 16 2023: (Start)
%F A210679 Additive with a(p^e) = 1 if p <= 7, and 0 otherwise.
%F A210679 a(n) = A001221(A165743(n)).
%F A210679 Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 247/210. (End)
%t A210679 Join[{0},Table[Count[FactorInteger[n][[All,1]],_?(#<8&)],{n,2,100}]] (* _Harvey P. Dale_, Aug 18 2021 *)
%t A210679 a[n_] := PrimeNu[GCD[n, 210]]; Array[a, 100] (* _Amiram Eldar_, Sep 16 2023 *)
%o A210679 (Haskell)
%o A210679 a210679 = length . takeWhile (<= 7) . a027748_row
%o A210679 (PARI) a(n) = omega(gcd(n, 210)); \\ _Amiram Eldar_, Sep 16 2023
%Y A210679 Cf. A001221, A002473, A008364, A027748, A080672, A165743.
%Y A210679 Number of distinct prime factors <= p: A171182 (p=3), A178146 (p=5), this sequence (p=7).
%K A210679 nonn,easy
%O A210679 1,6
%A A210679 _Reinhard Zumkeller_, Apr 01 2012