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A083676 Triangular numbers whose sum of aliquot divisors is a prime number. 1

%I

%S 21,55,171,325,595,741,1081,1711,2485,3081,3655,7021,11325,13861,

%T 14365,15931,23005,23653,23871,29403,31375,32131,44551,45451,48205,

%U 52003,53301,60031,65341,65703,67161,74691,81003,87571,92665,108811,110215,114481,115921

%N Triangular numbers whose sum of aliquot divisors is a prime number.

%H Donovan Johnson, <a href="/A083676/b083676.txt">Table of n, a(n) for n = 1..1000</a>

%H Shyam Sunder Gupta, <a href="http://www.shyamsundergupta.com/triangle.htm">Fascinating Triangular Numbers</a>.

%e a(2) = 55 because sum of aliquot divisors of 55 = 1+5+11 = 17, which is a prime number.

%o (PARI) c=0; for(m=1, 34021, t=m*(m+1)\2; if(isprime(sigma(t)-t), c++; write("b083676.txt", c " " t))) /* _Donovan Johnson_, May 20 2013 */

%K nonn

%O 1,1

%A _Shyam Sunder Gupta_, Jun 15 2003

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Last modified September 25 09:40 EDT 2021. Contains 347654 sequences. (Running on oeis4.)