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A062700
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Terms of A000203 that are prime.
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19
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3, 7, 13, 31, 31, 127, 307, 1093, 1723, 2801, 3541, 8191, 5113, 8011, 10303, 19531, 17293, 28057, 30941, 30103, 131071, 88741, 86143, 147073, 524287, 292561, 459007, 492103, 797161, 552793, 579883, 598303, 684757, 704761, 732541, 735307
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OFFSET
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1,1
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COMMENTS
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Sorted and duplicates removed, this gives A023195.
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LINKS
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FORMULA
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EXAMPLE
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sigma(2) = 3, sigma(4) = 7, sigma(9) = 13 are the first three prime terms of A000203. Hence the sequence starts 3, 7, 13.
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MATHEMATICA
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Select[DivisorSigma[1, Range[1000000]], PrimeQ] (* Harvey P. Dale, Nov 09 2012 *)
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PROG
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(Magma) [ c: n in [1..1000000] | IsPrime(c) where c:=SumOfDivisors(n) ]; // Klaus Brockhaus, Oct 21 2009
(PARI) je=[]; for(n=1, 1000000, if(isprime(sigma(n)), je=concat(je, sigma(n)))); je
(PARI) { n=0; for (m=1, 10^9, if(isprime(a=sigma(m)), write("b062700.txt", n++, " ", a); if (n==100, break)) ) } \\ Harry J. Smith, Aug 09 2009
(Python)
from sympy import isprime, divisor_sigma
A062700_list = [3]+[n for n in (divisor_sigma(d**2) for d in range(1, 10**4)) if isprime(n)] # Chai Wah Wu, Jul 23 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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