A378202 Largest primitive practical number that divides the n-th practical number - A005153(n).

1, 2, 2, 6, 2, 6, 2, 6, 20, 6, 28, 30, 2, 6, 20, 42, 6, 6, 28, 30, 2, 66, 6, 78, 20, 42, 88, 30, 6, 20, 104, 6, 28, 30, 42, 2, 66, 140, 6, 30, 78, 20, 6, 42, 88, 30, 6, 28, 66, 20, 204, 104, 210, 6, 220, 28, 228, 78, 30, 42, 2, 260, 88, 30, 272, 276, 140, 6, 42, 30, 304, 306, 308, 104, 20, 6, 330, 42, 340, 342, 348, 88, 30, 364, 368, 42, 380, 6, 390, 28, 66

Offset: 1

Author

Frank M Jackson, Nov 19 2024

Keywords

• nonn

Comments

Every practical number has a primitive practical divisor. a(n) is the largest primitive practical number that divides A005153(n). The quotient of A005153(n)/a(n) is A377377(n).

Examples

			a(8) = 6 because A005153(8) = 18 and the largest primitive practical that divides 18 is 6.
		

Crossrefs

Cf. A005153, A267124, A377377.

Programs

Mathematica

plst=Last/@ReadList["https://oeis.org/A005153/b005153.txt", {Number, Number}]; pplst=Last/@ReadList["https://oeis.org/A267124/b267124.txt", {Number, Number}]; getpplst[n_] := Module[{}, Select[pplst, #<=n &]]; lst1={}; Do[lst=getpplst[plst[[n]]]; lnh=Length@lst; m = 0; While[!IntegerQ[j=plst[[n]]/(k=lst[[lnh-m]])], m++]; AppendTo[lst1, {k, j}], {n, 1, 100}]; First/@lst1