cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A013932 Integers that are squarefree and also the sum of first k squarefrees for some k.

Original entry on oeis.org

1, 3, 6, 11, 17, 34, 58, 87, 123, 166, 215, 274, 305, 407, 482, 521, 562, 647, 791, 899, 1073, 1261, 1327, 1394, 1463, 1533, 1677, 1751, 1906, 1985, 2067, 2235, 2321, 2497, 2681, 2870, 2967, 3170, 3273, 3378, 3810, 3921, 4034, 4381, 4622, 4745, 5001, 5131, 5262
Offset: 1

Views

Author

Henri Lifchitz

Keywords

Links

Crossrefs

Cf. A005117, A013930, A013931, A020643, A173143.

Programs

  • Mathematica
    Select[Accumulate[Select[Range[150],SquareFreeQ]],SquareFreeQ] (* Harvey P. Dale, Jul 27 2011 *)
  • PARI
    lista(nn) = {my(s=0); for(k=1, nn, if(issquarefree(k)==1, s+=k; if(issquarefree(s)==1, print1(s, ", ")))); } \\ Jinyuan Wang, Feb 26 2020

Formula

a(n) = A005117(A020643(n)). - Amiram Eldar, Aug 19 2025

Extensions

More terms from Jinyuan Wang, Feb 26 2020

A013930 Sum of first a(n) squarefrees is squarefree.

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 9, 11, 13, 15, 17, 19, 20, 23, 25, 26, 27, 29, 32, 34, 37, 40, 41, 42, 43, 44, 46, 47, 49, 50, 51, 53, 54, 56, 58, 60, 61, 63, 64, 65, 69, 70, 71, 74, 76, 77, 79, 80, 81, 82, 83, 84, 86, 88, 89, 90, 92, 94, 95, 96, 98, 100, 102, 103, 104, 106, 107, 108, 110, 111
Offset: 1

Views

Author

Henri Lifchitz

Keywords

Links

Crossrefs

Cf. A005117, A013931, A013932.

Programs

Extensions

More terms from David W. Wilson

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

Original entry on oeis.org

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

Views

Author

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

Keywords

Links

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
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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