login
Primes whose 10's complement is a triangular number.
1

%I #11 Dec 15 2017 17:36:12

%S 7,79,97,139,439,769,829,997,1999,3559,6679,6997,7789,9439,9649,9769,

%T 9829,20599,25309,32839,34297,36097,42709,44389,49279,49597,56929,

%U 64489,65809,72739,76129,79699,82609,84247,86959,89269,89989,90547,93097

%N Primes whose 10's complement is a triangular number.

%H Harvey P. Dale, <a href="/A082992/b082992.txt">Table of n, a(n) for n = 1..250</a>

%t tctnQ[n_]:=Module[{c=1+FromDigits[9-IntegerDigits[n]]},IntegerQ[ (Sqrt[8c+1]-1)/2]]; Select[Prime[Range[10000]],tctnQ] (* _Harvey P. Dale_, Sep 21 2012 *)

%K nonn,base

%O 1,1

%A _Jason Earls_, May 31 2003