A352908 - OEIS

%I #41 Apr 16 2022 05:26:01

%S 3,4,5,13,21,36,37,57,61,70,73,93,100,129,130,154,157,193,201,205,217,

%T 237,250,253,277,301,310,313,322,333,381,397,406,417,421,442,453,457,

%U 493,513,517,541,565,597,603,613,646,661,673,682,685,697,733,757,781,813,826,877,913,921,925,994

%N Numbers k such that A232324(k) is prime.

%C Numbers k such that the k-th triangular number mod the sum of divisors of k is prime.

%H Robert Israel, <a href="/A352908/b352908.txt">Table of n, a(n) for n = 1..10000</a>

%e a(5) = 21 is a term because A232324(21) = 231 mod 32 = 7 is prime.

%p filter:= n -> isprime((n*(n+1)/2) mod numtheory:-sigma(n)):

%p select(filter, [$1..1000]);

%Y Contains A005383.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Apr 14 2022