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Search: id:A069708
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| A069708 |
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Triangular numbers with property that swapping first and last digits also gives a triangular number. |
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+0
3
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| 1, 3, 6, 10, 55, 66, 120, 153, 171, 190, 300, 351, 595, 630, 666, 820, 1081, 1431, 1711, 1891, 3003, 3403, 5050, 5460, 5565, 5995, 6216, 6786, 8128, 8778, 10011, 10731, 11781, 12561, 13041, 13861, 15051, 15931, 16471, 17020, 17391, 17578, 18721
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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820 and 028 = 28 both are triangular numbers hence both are members.
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MATHEMATICA
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Do[t = IntegerDigits[n(n + 1)/2]; u = t; u[[1]] = t[[ -1]]; u[[ -1]] = t[[1]]; t = FromDigits[u]; u = Floor[ Sqrt[2t]]; If[ u(u + 1)/2 == t, Print[n(n + 1)/2]], {n, 1, 300}]
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CROSSREFS
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Cf. A069706, A069707.
Sequence in context: A048089 A081975 A160965 this_sequence A061455 A068071 A067269
Adjacent sequences: A069705 A069706 A069707 this_sequence A069709 A069710 A069711
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KEYWORD
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nonn,base
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 08 2002
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EXTENSIONS
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Edited, corrected and extended by Robert G. Wilson v
Edited by N. J. A. Sloane (njas(AT)research.att.com), Jan 20 2009
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