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A144552
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Triangular numbers n*(n+1)/2 such that the three numbers n, n+1 and A001222(n)+A001222(n+1) are all composite.
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1
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45, 105, 120, 231, 300, 325, 378, 561, 595, 630, 741, 780, 990, 1485, 1540, 1596, 1653, 2016, 2080, 2850, 3240, 3321, 3570, 3655, 3741, 3828, 4095, 4371, 4465, 4560, 4851, 6786, 7021, 7381, 7503, 7750, 8256, 8778, 8911, 9045, 9180, 9870, 10011, 10153
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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MAPLE
| A001222 := proc(n) numtheory[bigomega](n) ; end: isA144552 := proc(n) if A001222(n) <= 1 or A001222(n+1) <= 1 then RETURN(false) ; fi; if not isprime(A001222(n)+A001222(n+1)) then true; else false; fi; end: for n from 0 to 200 do if isA144552(n) then printf("%d, ", n*(n+1)/2) ; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 03 2009]
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CROSSREFS
| Cf. A002808, A141468. See A144581 for another version.
Sequence in context: A118090 A063069 A067828 * A068355 A144486 A199351
Adjacent sequences: A144549 A144550 A144551 * A144553 A144554 A144555
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KEYWORD
| nonn
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AUTHOR
| Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Dec 31
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EXTENSIONS
| Edited (and 1596 inserted) by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 03 2009
Edited by N. J. A. Sloane (njas(AT)research.att.com), Jan 08 2009
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