cp's OEIS Frontend

A259745 Triangular numbers representable as x*y+x+y such that x and y are triangular numbers, x>=y>0.

%I A259745 #7 Aug 11 2015 15:50:34
%S A259745 3,15,21,91,120,153,351,406,703,741,1891,3081,3403,4465,5151,5565,
%T A259745 6555,9453,9591,18721,22791,23871,38226,39903,46056,52326,79401,85491,
%U A259745 91378,104653,159895,187578,207690,222111,227475,229503,266815,274911,280875,326028,334971,354903
%N A259745 Triangular numbers representable as x*y+x+y such that x and y are triangular numbers, x>=y>0.
%C A259745 A subsequence of A000217.
%C A259745 Up to 10^12, only 4 terms admit two representations, namely 3081, 22791, 410871 and 1675365. - _Giovanni Resta_, Jul 19 2015
%H A259745 Giovanni Resta, <a href="/A259745/b259745.txt">Table of n, a(n) for n = 1..509</a> (terms < 10^12)
%e A259745 a(1) = 3 = 1*1 + 1 + 1.
%e A259745 a(2) = 15 = 3*3 + 3 + 3.
%e A259745 a(3) = 21 = 10*1 + 10 + 1.
%e A259745 a(4) = 91 = 45*1 + 45 + 1.
%e A259745 a(5) = 120 = 10*10 + 10 + 10.
%e A259745 a(6) = 153 = 6*21 + 6 + 21.
%Y A259745 Cf. A000217, A259746.
%K A259745 nonn
%O A259745 1,1
%A A259745 _Alex Ratushnyak_, Jul 04 2015