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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A248792 Numbers n such that sigma(n) - 1 is a prime p. 7
 2, 3, 5, 6, 7, 10, 11, 13, 14, 15, 17, 19, 20, 21, 23, 24, 26, 29, 30, 31, 33, 34, 35, 37, 38, 40, 41, 43, 44, 46, 47, 51, 52, 53, 55, 57, 58, 59, 60, 61, 63, 65, 67, 71, 73, 74, 76, 78, 79, 83, 84, 85, 86, 88, 89, 90, 92, 93, 96, 97, 101, 103, 105, 107, 109 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Union of primes (A000040) and terms of A066073 (composites). Numbers n such that A039653(n) is prime. Corresponding values of primes p are in A248793. LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE 6 is in sequence because sigma(6) - 1 = 12 - 1 = 11 (prime). MAPLE with(numtheory): A248792:=n->`if`(isprime(sigma(n)-1), n, NULL): seq(A248792(n), n=1..200); # Wesley Ivan Hurt, Jul 09 2015 MATHEMATICA Select[Range[110], PrimeQ[DivisorSigma[1, #] - 1] &] (* Vincenzo Librandi, Nov 02 2014 *) PROG (MAGMA) [n: n in[1..1000] | IsPrime(SumOfDivisors(n) - 1)] (PARI) for(n=1, 10^3, if(isprime(sigma(n)-1), print1(n, ", "))) \\ Derek Orr, Nov 01 2014 CROSSREFS Cf. A000203 (sum of divisors), A000040 (primes). Cf. A039653 (sigma(n)-1), A066073 (subsequence of composites), A248793. Cf. A065512 (numbers n such that sigma(n) + 1 is prime). Sequence in context: A048839 A122144 A064052 * A064594 A325511 A240370 Adjacent sequences:  A248789 A248790 A248791 * A248793 A248794 A248795 KEYWORD nonn,easy AUTHOR Jaroslav Krizek, Nov 01 2014 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.

Last modified May 11 21:35 EDT 2021. Contains 343808 sequences. (Running on oeis4.)