

A283235


Triangle read by rows: nth row gives the numbers of primes p such that p*prime(k) <= prime(n)^2, k=1..n.


1



1, 2, 2, 5, 4, 3, 9, 6, 4, 4, 17, 12, 9, 7, 5, 23, 16, 11, 9, 6, 6, 34, 24, 16, 13, 9, 8, 7, 41, 30, 20, 15, 11, 9, 8, 8, 56, 40, 27, 21, 15, 12, 11, 9, 9, 81, 59, 39, 30, 21, 18, 15, 14, 11, 10
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OFFSET

1,2


COMMENTS

Sequence is related to A128301 = indices of squares (of primes) in the semiprimes.


LINKS



EXAMPLE

Triangle begins:
1;
2, 2;
5, 4, 3;
9, 6, 4, 4;
17, 12, 9, 7, 5;
23, 16, 11, 9, 6, 6;
34, 24, 16, 13, 9, 8, 7;
41, 30, 20, 15, 11, 9, 8, 8;
56, 40, 27, 21, 15, 12, 11, 9, 9;
81, 59, 39, 30, 21, 18, 15, 14, 11, 10;
...


MATHEMATICA

Table[PrimePi[Prime[n]^2/Prime[k]], {n, 10}, {k, n}]//Flatten


PROG

(PARI) row(n) = my(p=prime(n)); vector(n, k, primepi(p^2/prime(k))); \\ Michel Marcus, Nov 01 2021


CROSSREFS



KEYWORD



AUTHOR



STATUS

approved



