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

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

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: A369185 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