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A144552 Triangular numbers n*(n+1)/2 such that the three numbers n, n+1 and A001222(n) + A001222(n+1) are all composite. 2
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; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..2000

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: # R. J. Mathar, Jan 03 2009

MATHEMATICA

Times@@#/2&/@Select[Partition[Select[Range[200], CompositeQ], 2, 1], #[[2]]- #[[1]] == 1&&CompositeQ[Total[PrimeOmega[#]]]&] (* Harvey P. Dale, Jun 05 2017 *)

CROSSREFS

Cf. A002808, A141468. See A144581 for another version.

Sequence in context: A247887 A063069 A067828 * A068355 A331190 A332593

Adjacent sequences:  A144549 A144550 A144551 * A144553 A144554 A144555

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Dec 31 2008

EXTENSIONS

Edited (and 1596 inserted) by R. J. Mathar, Jan 03 2009

Edited by N. J. A. Sloane, Jan 08 2009

STATUS

approved

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Last modified May 7 20:36 EDT 2021. Contains 343652 sequences. (Running on oeis4.)