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

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, 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, 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

Offset

4,5

Comments

This triangle consists of those columns of A278108 with prime index.

The row length sequence is A056811.

Links

Jason Kimberley, Table of i, a(i) for i = 4..7656 (T(n,k) for n = 4..1000)

Formula

T(n,k) = A278108(n,A000040(k)).

Example

The initial rows (for n = 4..27) are:
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, 2;
6, 2;
6, 2, 1;
6, 2, 1;
6, 3, 1;

Prog

(Magma) [n div p^2:p in PrimesUpTo(Isqrt(n)), n in[1..45]];

Crossrefs

Cf. A056811, A277648, A278108, A278110.

Sequence in context: A344339 A348364 A279620 * A216665 A301384 A258124

Adjacent sequences: A278106 A278107 A278108 * A278110 A278111 A278112

Keyword

nonn,easy,tabf

Author

Jason Kimberley, Feb 02 2017

Status

approved