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A278109
Irregular triangle read by rows: T(n,k) = floor(n/prime(k)^2) for 1 <= prime(k)^2 <= n.
3
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.
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
KEYWORD
nonn,easy,tabf
AUTHOR
Jason Kimberley, Feb 02 2017
STATUS
approved