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A283235
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Triangle read by rows: n-th row gives the numbers of primes p such that p*prime(k) <= prime(n)^2, k=1..n.
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1
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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
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1,2
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COMMENTS
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Sequence is related to A128301 = indices of squares (of primes) in the semiprimes.
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LINKS
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Table of n, a(n) for n=1..55.
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EXAMPLE
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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;
...
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MATHEMATICA
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Table[PrimePi[Prime[n]^2/Prime[k]], {n, 10}, {k, n}]//Flatten
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PROG
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(PARI) row(n) = my(p=prime(n)); vector(n, k, primepi(p^2/prime(k))); \\ Michel Marcus, Nov 01 2021
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CROSSREFS
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Cf. A128301, A348836 (1st column).
Sequence in context: A209771 A209751 A275381 * A209763 A209761 A228526
Adjacent sequences: A283232 A283233 A283234 * A283236 A283237 A283238
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KEYWORD
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nonn,tabl
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AUTHOR
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Zak Seidov, Mar 03 2017
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STATUS
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approved
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