cp's OEIS Frontend

A278109 Irregular triangle read by rows: T(n,k) = floor(n/prime(k)^2) for 1 <= prime(k)^2 <= n.

%I A278109 #9 Sep 08 2022 08:46:17
%S A278109 1,1,1,1,2,2,1,2,1,2,1,3,1,3,1,3,1,3,1,4,1,4,1,4,2,4,2,5,2,5,2,5,2,5,
%T A278109 2,6,2,6,2,1,6,2,1,6,3,1,7,3,1,7,3,1,7,3,1,7,3,1,8,3,1,8,3,1,8,3,1,8,
%U A278109 3,1,9,4,1,9,4,1,9,4,1,9,4,1,10,4,1,10,4,1,10,4,1,10,4,1,11,4,1,11,5,1
%N A278109 Irregular triangle read by rows: T(n,k) = floor(n/prime(k)^2) for 1 <= prime(k)^2 <= n.
%C A278109 This triangle consists of those columns of A278108 with prime index.
%C A278109 The row length sequence is A056811.
%H A278109 Jason Kimberley, <a href="/A278109/b278109.txt">Table of i, a(i) for i = 4..7656 (T(n,k) for n = 4..1000)</a>
%F A278109 T(n,k) = A278108(n,A000040(k)).
%e A278109 The initial rows (for n = 4..27) are:
%e A278109 1;
%e A278109 1;
%e A278109 1;
%e A278109 1;
%e A278109 2;
%e A278109 2, 1;
%e A278109 2, 1;
%e A278109 2, 1;
%e A278109 3, 1;
%e A278109 3, 1;
%e A278109 3, 1;
%e A278109 3, 1;
%e A278109 4, 1;
%e A278109 4, 1;
%e A278109 4, 2;
%e A278109 4, 2;
%e A278109 5, 2;
%e A278109 5, 2;
%e A278109 5, 2;
%e A278109 5, 2;
%e A278109 6, 2;
%e A278109 6, 2, 1;
%e A278109 6, 2, 1;
%e A278109 6, 3, 1;
%o A278109 (Magma) [n div p^2:p in PrimesUpTo(Isqrt(n)),n in[1..45]];
%Y A278109 Cf. A056811, A277648, A278108, A278110.
%K A278109 nonn,easy,tabf
%O A278109 4,5
%A A278109 _Jason Kimberley_, Feb 02 2017