login
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
OFFSET
1,1
LINKS
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
KEYWORD
nonn
AUTHOR
EXTENSIONS
Edited (and 1596 inserted) by R. J. Mathar, Jan 03 2009
Edited by N. J. A. Sloane, Jan 08 2009
STATUS
approved