login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

OEIS Wiki, Cyclotomic Polynomials at x=n, n! and sigma(n)

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

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