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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 July 20 17:32 EDT 2024. Contains 374459 sequences. (Running on oeis4.)