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Numbers n divisible by the largest prime < sqrt(n), A007917(A000196(n-1)).
4

%I #10 Jul 25 2024 14:08:47

%S 6,8,12,15,18,21,24,30,35,40,45,56,63,70,77,84,91,98,105,112,119,132,

%T 143,154,165,182,195,208,221,234,247,260,273,286,306,323,340,357,380,

%U 399,418,437,456,475,494,513,552,575,598,621,644,667,690,713,736,759

%N Numbers n divisible by the largest prime < sqrt(n), A007917(A000196(n-1)).

%C Includes products of pairs of consecutive primes (A006094) as subsequence, equals A157942 with squares of primes (A001248) removed.

%C For a number < 5 the definition does not make much sense, since there is no prime < sqrt(4) = 2, so we don't consider them here.

%H Harvey P. Dale, <a href="/A157941/b157941.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[6,800],Divisible[#,NextPrime[Sqrt[#],-1]]&] (* _Harvey P. Dale_, Sep 14 2019 *)

%o (PARI) for( n=5,999, n % precprime(sqrtint(n-1)) || print1(n","))

%K nonn

%O 1,1

%A _M. F. Hasler_, Mar 09 2009