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A116541
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Triangular numbers for which the number of divisors is also a triangular number.
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0
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1, 28, 45, 153, 171, 325, 496, 2016, 3321, 4753, 4950, 7260, 7381, 8256, 11628, 13203, 14196, 20100, 29161, 41616, 56953, 64620, 65341, 73536, 76636, 77028, 89676, 90100, 97461, 101475, 126756, 130816, 150975, 166176, 166753, 179700, 180300
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| 496 is in the sequence because it is a triangular number (31*32/2) and has 10=4*5/2 divisors (1,2,4,8,16,31,62,124,248,496).
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MAPLE
| with(numtheory): a:=proc(n) local s: s:=tau(n*(n+1)/2): if type(sqrt(1+8*s)/2-1/2, integer)=true then n*(n+1)/2 else fi end: seq(a(n), n=1..750); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 06 2006
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MATHEMATICA
| Select[ Range(AT)600/2*(Range(AT)600 + 1), IntegerQ(AT) Sqrt[8DivisorSigma[0, # ] + 1] &] (from Robert G. Wilson v (rgwv(at)rgwv.com), Apr 20 2006).
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CROSSREFS
| Sequence in context: A180045 A144581 A075875 * A116565 A039615 A046419
Adjacent sequences: A116538 A116539 A116540 * A116542 A116543 A116544
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KEYWORD
| nonn
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AUTHOR
| Luc Stevens (lms022(AT)yahoo.com), Apr 03 2006
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 06 2006
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