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A133198 Triangular numbers such that moving the last digit to the front produces a square number. 2
1, 10, 3240, 464166, 1043290, 5740966, 335936160, 428264011, 3529890253, 4015289691, 108170400250, 821266581691, 2216062991691, 34830532944360, 2453718234672253, 6017966241009003, 11215323437683690, 214486304402280015, 446417240103777645, 1792095001020995616 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..100

EXAMPLE

3240 is a triangular number, 0324 is a square number - hence 3240 belongs to this sequence.

MAPLE

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, Oct 17 2007

MATHEMATICA

Select[Table[n(n + 1)/2, {n, 1000000}], IntegerQ[Sqrt[ FromDigits[ Prepend[Drop[IntegerDigits[ # ], -1], Last[IntegerDigits[ # ]]]]]] &]

CROSSREFS

Cf. A133197.

Sequence in context: A061543 A225764 A243008 * A001329 A007101 A007103

Adjacent sequences:  A133195 A133196 A133197 * A133199 A133200 A133201

KEYWORD

base,nonn

AUTHOR

Tanya Khovanova, Oct 09 2007

EXTENSIONS

More terms from Emeric Deutsch, Oct 17 2007

Offset corrected and a(15)-a(19) from Donovan Johnson, Jan 31 2011

a(20) from Giovanni Resta, May 11 2016

STATUS

approved

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Last modified June 29 01:28 EDT 2017. Contains 288855 sequences.