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A065404
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Squares of composite numbers n such that sigma[n] (sum of divisors of n, A000203) is a prime.
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2
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16, 64, 729, 2401, 4096, 15625, 28561, 65536, 83521, 262144, 279841, 531441, 707281, 3418801, 4826809, 9765625, 24137569, 28398241, 38950081, 47458321, 244140625, 260144641, 887503681, 1073741824, 1387488001, 2655237841
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,100
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FORMULA
| Sigma[A065404(n)] = Sigma[a(n)] = A065403(n) = A000203[A065404(n)].
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EXAMPLE
| 46 cases below 10^12; for M a Mersenne prime, (M+1)/2 is here: M=8191,4096=(M+1)/2.
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PROG
| (PARI) { n=0; for (m=1, 10^9, if (isprime(m), next); x=sigma(m^2); if (isprime(x), write("b065404.txt", n++, " ", m^2); if (n==100, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Oct 18 2009]
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CROSSREFS
| Cf. A062700, A000203, A065403-A065405, A053182, A053183, A028982.
Sequence in context: A175209 A141840 A203281 * A189806 A031446 A041492
Adjacent sequences: A065401 A065402 A065403 * A065405 A065406 A065407
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Nov 06 2001
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