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 A259185 Numbers n such that 1 - sigma(n) + sigma(n)^2 is prime. 3
 2, 3, 4, 5, 8, 9, 10, 12, 17, 18, 20, 24, 26, 30, 32, 36, 38, 40, 41, 45, 46, 51, 54, 55, 56, 58, 59, 60, 66, 70, 71, 72, 78, 86, 87, 89, 91, 92, 94, 95, 99, 101, 102, 104, 106, 108, 110, 115, 116, 119, 123, 125, 131, 134, 138, 142, 143, 144, 154, 159, 164 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Price, Table of n, a(n) for n = 1..1737 MAPLE with(numtheory): A259185:=n->`if`(isprime(1 - sigma(n) + sigma(n)^2), n, NULL): seq(A259185(n), n=1..500); # Wesley Ivan Hurt, Jul 09 2015 MATHEMATICA Select[ Range[10000], PrimeQ[ 1 - DivisorSigma[1, n] + DivisorSigma[1, n]^2] & ] Select[ Range[10000], PrimeQ[ Cyclotomic[6, DivisorSigma[1, #]]] &] PROG (MAGMA) [n: n in [1..180] | IsPrime(1 - SumOfDivisors(n) + SumOfDivisors(n)^2)]; // Vincenzo Librandi, Nov 20 2015 (PARI) is(n)=my(s=sigma(n)); isprime(s^2-s+1) \\ Charles R Greathouse IV, May 22 2017 CROSSREFS Cf. A000203, A259184, A259186. Sequence in context: A005792 A270430 A318932 * A102471 A243490 A094566 Adjacent sequences:  A259182 A259183 A259184 * A259186 A259187 A259188 KEYWORD nonn,easy AUTHOR Robert Price, Jun 20 2015 STATUS approved

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Last modified September 19 22:06 EDT 2021. Contains 347576 sequences. (Running on oeis4.)