OFFSET
1,1
EXAMPLE
a(1) = 7 because SP(1) = semiprime(1) = 4, Triangular number T(7) = 7*(7+1)/2 = 28 and 7 divides 28.
a(2) = 3 because SP(2) = 6 | T(3) = 6.
a(3) = 8 because SP(3) = 9 | T(8) = 36.
a(9) = 24 because SP(9) = 25 | T(24) = 300.
a(17) = 48 because SP(17) = 49 | T(48) = 1176.
MATHEMATICA
a = Select[Range@215, Plus @@ Last /@ FactorInteger@# == 2 &]; f[n_] := Block[{k = 1}, While[ Mod[k(k + 1)/2, a[[n]]] > 0, k++ ]; k]; Array[f, 71] (* Robert G. Wilson v *)
Module[{nn=500, trno, smpr, k}, trno=Accumulate[Range[nn]]; smpr=Select[Range[ nn], PrimeOmega[ #] == 2&]; Table[ k= SelectFirst[ trno, Mod[ #, smpr[[n]]]==0&]; (Sqrt[8k+1]-1)/2, {n, Length[ smpr]}]] (* Harvey P. Dale, Jul 09 2024 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Mar 08 2006
EXTENSIONS
More terms from Robert G. Wilson v, May 01 2006
STATUS
approved