A020643 a(n)-th squarefree is sum of first k squarefrees for some k.

1, 3, 5, 8, 12, 22, 36, 55, 77, 102, 133, 169, 187, 248, 296, 320, 343, 395, 483, 547, 652, 768, 809, 851, 893, 935, 1023, 1065, 1158, 1206, 1256, 1359, 1412, 1522, 1631, 1746, 1805, 1932, 1992, 2057, 2316, 2385, 2454, 2665, 2812, 2887, 3043, 3119, 3199, 3279

Offset: 1

Author

N. J. A. Sloane, Renaud Lifchitz (100637.64(AT)CompuServe.COM), and David W. Wilson

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A005117, A013930, A013931, A013932.

Programs

Mathematica

With[{s = Select[Range[6000], SquareFreeQ]}, Position[s, #] & /@ Select[Accumulate[s], # <= s[[-1]] && SquareFreeQ[#] &] // Flatten] (* Amiram Eldar, Aug 19 2025 *)

Formula

A005117(a(n)) = A013932(n). - Amiram Eldar, Aug 19 2025