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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
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 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..55.

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

Cf. A128301, A348836 (1st column).

Sequence in context: A209771 A209751 A275381 * A209763 A209761 A228526

Adjacent sequences: A283232 A283233 A283234 * A283236 A283237 A283238

KEYWORD

nonn,tabl

AUTHOR

Zak Seidov, Mar 03 2017

STATUS

approved

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Last modified January 29 11:19 EST 2023. Contains 359922 sequences. (Running on oeis4.)