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 A066569 Triangular numbers whose reverse is also triangular. 2

%I

%S 1,3,6,55,66,153,171,351,595,666,3003,5995,8778,15051,17578,66066,

%T 87571,185745,547581,617716,828828,1269621,1461195,1680861,3544453,

%U 5073705,5676765,5911641,6295926,12145056,12517506,35133153,60571521

%N Triangular numbers whose reverse is also triangular.

%C Numbers ending in 0 are not included. - _Harry J. Smith_, Mar 06 2010

%H Harry J. Smith, <a href="/A066569/b066569.txt">Table of n, a(n) for n = 1..100</a>

%e 153 and 351 are both triangular.

%t dtn[L_] := Fold[10#1+#2&, 0, L] tritest[n_] := Module[{t}, t=Floor[N[Sqrt[2n]]]; 2n==t(t+1)] A={}; For[i=1, i>0, i++, t=i(i+1)/2; If[tritest[dtn[Reverse[IntegerDigits[t]]]]&&Mod[t, 10]>0, AppendTo[A, t]; Print[A]]]

%t Select[Accumulate[Range[12000]],Last[IntegerDigits[#]]!=0&&OddQ[Sqrt[1+ 8*FromDigits[Reverse[IntegerDigits[#]]]]]&] (* _Harvey P. Dale_, Jun 04 2015 *)

%o (PARI) Rev(x)= { local(d, r=0); while (x>0, d=x%10; x\=10; r=r*10 + d); return(r) } { n=0; for (m=1, 10^10, t=m*(m + 1)/2; if (t%10 == 0, next); if (issquare(8*Rev(t) + 1), write("b066569.txt", n++, " ", t); if (n==100, return)) ) } \\ _Harry J. Smith_, Mar 08 2010

%K base,nonn

%O 1,2

%A _Erich Friedman_, Jan 08 2002

%E Offset changed from 0 to 1 by _Harry J. Smith_, Mar 06 2010

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Last modified January 25 07:24 EST 2020. Contains 331241 sequences. (Running on oeis4.)