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A066569
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Triangular numbers whose reverse is also triangular.
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2
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1, 3, 6, 55, 66, 153, 171, 351, 595, 666, 3003, 5995, 8778, 15051, 17578, 66066, 87571, 185745, 547581, 617716, 828828, 1269621, 1461195, 1680861, 3544453, 5073705, 5676765, 5911641, 6295926, 12145056, 12517506, 35133153, 60571521
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers ending in 0 are not included. [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 06 2010]
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,100
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EXAMPLE
| 153 and 351 are both triangular
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MATHEMATICA
| 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]]]
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PROG
| (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)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 08 2010]
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CROSSREFS
| Sequence in context: A023177 A132474 A032070 * A051641 A003098 A045914
Adjacent sequences: A066566 A066567 A066568 * A066570 A066571 A066572
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KEYWORD
| base,nonn
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AUTHOR
| Erich Friedman (efriedma(AT)stetson.edu), Jan 08 2002
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EXTENSIONS
| OFFSET changed from 0,2 to 1,2 by Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 06 2010
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