A283235 Triangle read by rows: n-th row gives the numbers of primes p such that p*prime(k) <= prime(n)^2, k=1..n.
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
Offset: 1
Examples
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; ...
Programs
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Mathematica
Table[PrimePi[Prime[n]^2/Prime[k]],{n,10},{k,n}]//Flatten -
PARI
row(n) = my(p=prime(n)); vector(n, k, primepi(p^2/prime(k))); \\ Michel Marcus, Nov 01 2021
Comments