A361506 a(n) = floor( (4/5)*( (9/4)^(n+1)-1 ) ).

1, 3, 8, 19, 45, 102, 232, 524, 1181, 2659, 5984, 13466, 30300, 68177, 153400, 345151, 776590, 1747330, 3931495, 8845865, 19903197, 44782195, 100759939, 226709865, 510097199, 1147718699, 2582367075, 5810325919, 13073233320, 29414774972, 66183243689, 148912298302

Offset: 0

Author

N. J. A. Sloane, Mar 20 2023, at the suggestion of Don Knuth

Keywords

• nonn

References

• N. Tokuda, An Improved Shellsort, IFIP Transactions, A-12 (1992) 449-457.

Links

• Marcin Ciura, Best Increments for the Average Case of Shellsort, in R. Freivalds, (ed.), Fundamentals of Computation Theory: 13th International Symposium, FCT 2001, Riga, Latvia, August 2001, Lecture Notes in Computer Science, vol. 2138, Springer, pp. 106-117.

Crossrefs

Other sequences used for Shell sort: A003462, A033622, A036562, A036564, A036569, A055875, A055876, A108870, A361507.

Programs

Mathematica

A361506[n_]:=Floor[4/5((9/4)^(n+1)-1)];Array[A361506,50,0] (* Paolo Xausa, Dec 02 2023 *)

Extensions

Some terms corrected by Paolo Xausa, Dec 02 2023