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A065893 Which composite number is the square of n? Index of n^2 in A002808. 2

%I

%S 0,1,4,9,15,24,33,45,58,74,90,109,129,151,176,201,227,257,288,321,355,

%T 391,429,470,510,553,599,646,694,745,798,851,907,964,1024,1085,1149,

%U 1215,1280,1348,1417,1489,1565,1640,1718,1796,1879,1961,2043,2132,2222

%N Which composite number is the square of n? Index of n^2 in A002808.

%H Harry J. Smith, <a href="/A065893/b065893.txt">Table of n, a(n) for n = 1..1000</a>

%e n = 5 and 25 is the 15th composite number: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25.

%t Table[n^2-(PrimePi[n^2])-1, {w, 1, 128}]

%o (PARI) { default(primelimit, 4294965247); for (n=1, 1000, f=n^2; a=f - primepi(f) - 1; write("b065893.txt", n, " ", a) ) } \\ _Harry J. Smith_, Nov 04 2009

%Y Cf. A002808, A000290, A000720.

%K nonn

%O 1,3

%A _Labos Elemer_, Nov 28 2001

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Last modified June 15 18:33 EDT 2021. Contains 345049 sequences. (Running on oeis4.)