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A061455
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Triangular numbers whose digit reversal is also a triangular number.
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1
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0, 1, 3, 6, 10, 55, 66, 120, 153, 171, 190, 300, 351, 595, 630, 666, 820, 3003, 5995, 8778, 15051, 17578, 66066, 87571, 156520, 180300, 185745, 547581, 557040, 617716, 678030, 828828, 1269621, 1461195, 1680861, 1851850, 3544453, 5073705, 5676765
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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FORMULA
| a(n)=A000217(k) and A004086(a(n))=A000217(j) for some k and j. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 02 2006
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EXAMPLE
| 153 is in the sequence because (1) it is a triangular number and (2) the reversal 351 is also a triangular number.
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MAPLE
| read("transforms");
isA000217 := proc(n) issqr(1+8*n) ; end proc:
isA061455 := proc(n) isA000217(n) and isA000217(digrev(n)) ; end proc:
for n from 0 to 60000 do T := A000217(n) ; if isA061455(T) then printf("%d, ", T) ; end if; end do: # R. J. Mathar(AT)strw.leidenuniv.nl), Dec 13 2010
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MATHEMATICA
| TriangularNumberQ[k_] := If[IntegerQ[1/2 (Sqrt[1 + 8 k] - 1)], True, False]; Select[Range[0, 5676765], TriangularNumberQ[#] && TriangularNumberQ[FromDigits[Reverse[IntegerDigits[#]]]] &] (*from Ant King 13 Dec 2010*)
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CROSSREFS
| Cf. A000217.
Sequence in context: A081975 A160965 A069708 * A068071 A067269 A071299
Adjacent sequences: A061452 A061453 A061454 * A061456 A061457 A061458
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KEYWORD
| nonn,base,easy
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), May 03 2001
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EXTENSIONS
| More terms from Erich Friedman (efriedma(AT)stetson.edu), May 08 2001
Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 13 2008 at the suggestion of R. J. Mathar.
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