A339864 - OEIS

%I #12 Jan 31 2021 11:38:36

%S 3,19,29,41,59,103,131,139,151,149,229,211,269,349,269,389,439,383,

%T 523,419,449,727,701,787,569,683,719,659,991,859,811,1009,887,1153,

%U 877,1109,1489,1489,1223,1327,1657,1579,1259,1693,2221,1409,2011,1607,1831,2251,1867,2503,1801,1811,2677,2689

%N Primes of the form p + sigma(p-1) for primes p.

%C Terms are in order of increasing p.

%C Terms that occur more than once include 269, 1489, 2903, 3271, 5099, 7159.

%H Robert Israel, <a href="/A339864/b339864.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A339862(n) + sigma(A339862(n)-1).

%e A339862(3) = 11 so a(3) = 11 + sigma(11-1) = 29.

%p select(isprime, map(t -> t + numtheory:-sigma(t-1), [seq(ithprime(i),i=1..200)]));

%t Select[#+DivisorSigma[1,#-1]&/@Prime[Range[200]],PrimeQ] (* _Harvey P. Dale_, Jan 31 2021 *)

%Y Cf. A000203, A339882.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Dec 19 2020

%E Definition clarified by _Harvey P. Dale_, Jan 31 2021