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 A219603 a(n) = prime(n) * prime(2*n-1). 4

%I

%S 4,15,55,119,253,403,697,893,1357,1943,2263,3071,3977,4429,5123,6731,

%T 8083,9089,10519,11857,13067,15089,16351,18779,22019,23533,24823,

%U 27499,29321,31301,35941,40217,42881,46009,51703,53303,57619,61777,64963,69373,75001

%N a(n) = prime(n) * prime(2*n-1).

%C A020639(a(n)) = A000040(n); A006530(a(n)) = A031368(n);

%C a(n) is central term of row 2n-1 of semiprimes triangle (A087112).

%H Reinhard Zumkeller, <a href="/A219603/b219603.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000040(n) * A031368(n).

%o a219603 n = a000040 n * a031368 n

%o (PARI) a(n)=prime(n) * prime(2*n-1) \\ _Charles R Greathouse IV_, Feb 07 2017

%Y Subsequence of A001358.

%Y Cf. A006094.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Nov 25 2012

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Last modified August 7 17:34 EDT 2020. Contains 336278 sequences. (Running on oeis4.)