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A094609
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Numbers n such that n concatenated with n+1 is triangular.
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0
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4, 7, 49, 52, 295, 369, 415, 499, 502, 594, 652, 760, 2254, 4999, 5002, 8827, 10330, 14877, 49999, 50002, 490150, 499999, 500002, 509949, 3347109, 4999999, 5000002, 6983470, 24913494, 49999999, 50000002
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Numbers 4, 49, 499, 4999, ...; 52, 502, 5002, 50002, ...; 594, 509949, 500999499, 500099994999, ...; 415, 490150, 499001500, 499900015000, ...; with obvious patterns are members of the sequence. - Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 09 2004
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EXAMPLE
| E.g. 5253 is triangular so 52 is a member.
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MATHEMATICA
| triQ[n_] := Block[{k = Floor[ Sqrt[2n]]}, If[ k(k + 1) == 2n, True, False]]; Do[ If[ triQ[ FromDigits[ Join[ IntegerDigits[n], IntegerDigits[n + 1]] ]] == True, Print[ n]], {n, 45000000}] (from Robert G. Wilson v Jun 09 2004)
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CROSSREFS
| Cf. A000217.
Sequence in context: A139030 A115439 A192168 * A049191 A013467 A060413
Adjacent sequences: A094606 A094607 A094608 * A094610 A094611 A094612
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KEYWORD
| base,nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Jun 06 2004
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 09 2004
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