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Search: id:A133198
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| A133198 |
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Triangular numbers such that moving the last digit to the front produces a square number. |
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+0
1
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| 1, 10, 3240, 464166, 1043290, 5740966, 335936160, 428264011, 3529890253, 4015289691, 108170400250, 821266581691, 2216062991691, 34830532944360
(list; graph; listen)
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OFFSET
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0,2
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EXAMPLE
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3240 is a triangular number, 0324 is a square number - hence 324 belongs to this sequence.
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MAPLE
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a:=proc(n) local n2, L: n2:=convert((1/2)*n*(n+1), base, 10): L:=nops(n2): if type(sqrt((1/20)*n*(n+1)-(1/10)*n2[1]+n2[1]*10^(L-1)), integer)=true then (1/2)*n*(n+1) else end if end proc: seq(a(n), n=1..10^7); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Oct 17 2007
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MATHEMATICA
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Select[Table[n(n + 1)/2, {n, 1000000}], IntegerQ[Sqrt[ FromDigits[ Prepend[Drop[IntegerDigits[ # ], -1], Last[IntegerDigits[ # ]]]]]] &]
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CROSSREFS
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Adjacent sequences: A133195 A133196 A133197 this_sequence A133199 A133200 A133201
Sequence in context: A132675 A123377 A061543 this_sequence A001329 A007101 A007103
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KEYWORD
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base,nonn
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AUTHOR
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Tanya Khovanova (tanyakh(AT)yahoo.com), Oct 09 2007
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Oct 17 2007
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