A065512 Numbers n such that sigma(n) + 1 is prime.
1, 3, 5, 6, 10, 11, 12, 17, 20, 22, 24, 26, 27, 29, 30, 38, 41, 42, 45, 46, 51, 55, 59, 62, 68, 69, 71, 77, 82, 85, 88, 91, 99, 101, 104, 105, 106, 107, 108, 114, 116, 118, 125, 126, 132, 135, 136, 137, 140, 141, 145, 146, 147, 149, 150, 155, 158, 160, 161
Offset: 1
Keywords
Examples
sigma(10) + 1 = 18 + 1 = 19 (prime). sigma(24) + 1 = 60 + 1 = 61 (prime).
Links
- Harry J. Smith, Table of n, a(n) for n=1..1000
- OEIS Wiki, Cyclotomic Polynomials at x=n, n! and sigma(n)
Programs
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Magma
[n: n in [1..200] | IsPrime(1+SumOfDivisors(n))]; // Vincenzo Librandi, May 30 2015
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Maple
select(isprime @ (1+numtheory:-sigma), [$1..1000]); # Robert Israel, May 29 2015
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Mathematica
Select[ Range[170], PrimeQ[ DivisorSigma[1, # ] + 1] & ]
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PARI
{ n=0; for (m=1, 10^9, if (isprime(sigma(m) + 1), write("b065512.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 20 2009