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 1-5 of 5 results.

A085265 Numbers that can be written as sum of a positive squarefree number and a positive square.

Original entry on oeis.org

2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71
Offset: 1

Views

Author

Reinhard Zumkeller, Jun 23 2003

Keywords

Comments

Subsequence of A011760; A085263(a(n)) > 0.
Conjecture: a(n) = n + 2 for n > 11. That is, only 1 and 13 are missing. - Charles R Greathouse IV, Aug 21 2011
Estermann proves that only finitely many positive integers are missing from this sequence. (Probably only 1 and 13.) - Charles R Greathouse IV, Jul 01 2016

Programs

  • PARI
    is(n)=forstep(k=sqrtint(n-1), 1, -1, if(issquarefree(n-k^2), return(1))); 0 \\ Charles R Greathouse IV, Mar 12 2012

A085266 Numbers having a unique representation as sum of a squarefree number and a square.

Original entry on oeis.org

2, 3, 4, 5, 8, 9, 25, 29, 61
Offset: 1

Views

Author

Reinhard Zumkeller, Jun 23 2003

Keywords

Comments

A085263(a(n))=1; are there more?
No more terms through 625000000. - Ryan Propper, Jan 05 2008

Crossrefs

A085267 Numbers having at least two representations as sum of a squarefree number and a nonzero square.

Original entry on oeis.org

6, 7, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 26, 27, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78
Offset: 1

Views

Author

Reinhard Zumkeller, Jun 23 2003

Keywords

Comments

Numbers n such that A085263(a(n)) > 1.
Conjecture: for n > 50, a(n) = n + 11. - Charles R Greathouse IV, Oct 26 2011

Crossrefs

Programs

  • PARI
    is(n)=my(t);forstep(k=sqrtint(n-1),1,-1,if(issquarefree(n-k^2),if(t++>1,return(1))));0 \\ Charles R Greathouse IV, Mar 12 2012

A085264 Smallest number with exactly n representations as sum of a squarefree number (A005117) and a square (A000290).

Original entry on oeis.org

1, 2, 6, 11, 23, 30, 38, 62, 71, 83, 110, 138, 155, 182, 203, 227, 263, 302, 327, 383, 435, 447, 503, 542, 602, 635, 707, 755, 798, 878, 915, 983, 1055, 1118, 1182, 1295, 1343, 1403, 1463, 1547, 1643, 1722, 1778, 1883, 1995, 2063, 2162, 2238, 2327
Offset: 0

Views

Author

Reinhard Zumkeller, Jun 23 2003

Keywords

Comments

A085263(a(n))=n and A085263(i)<>n for i
From Robert G. Wilson v, May 17 2014: (Start)
First occurrence of k, beginning with 0, in A085263.
Conjecture: Just as there is a least integer that can be represented in n ways, so is there a greatest integer.
Conjecture: The last occurrence of k, beginning with 0, in A085263: 13, 61, 85, 196, 225, 441, 621, 909, 1089, 1125, 1521, 2025, 2700, 2200, 2925, 3969, 3825, 4500, 5625, 4869, 6084, 8100, 11025, 7425, 9900, 9981, 10584, 11925, 12825, 14400, 13500, 14625, 18081, 18225, 17424, 20925, 22500, 27225, 21825, 25425, 27000, 28224, 27900, 38025, 44100, 33300, 35721, 35325, 39825, 37044, 39600, 40725, 44325, 55125, 50625, 53100, 52200, 54000, 60300, 65025, 63900, 60025, 63504, 64125, 74529, 81225, 77400, 99225, 88200, 76500, 79200, 87525, 90000, 108900, 88425, 91800, 95400, 96300, 100125, 107325, 132300, ..., .
Conjecture: For each j, there is a finite number of positive integers that can be represented as the sum of a squarefree number and a square in exactly j ways; e.g., for j=0, only the two integers 1 and 13 cannot be represented as the sum of a squarefree number and a square.
The number of integers that can be represented as the sum of a squarefree number and a square in j ways beginning with 0: 2, 9, 19, 27, 38, 36, 57, 63, 62, 74, 94, 86, 101, 112, 123, 113, 139, 140, 146, 170, 155, 202, 167, 196, 204, 213, 213, 215, 233, 232, 255, 249, 276, 261, 278, 310, 321, 300, 302, 336, 347, 325, 325, 350, 375, 367, 413, 393, 377, 384, 427, 435, 440, 447, 434, 472, 445, 476, 470, 518, 482, 499, 510, 542, 519, 550, 506, 553, 591, 572, 626, 586, 582, 585, 598, 623, 623, 656, 595, 697, 641, 672, 702, 689, 733, 696, 661, 718, 738, 757, 755, 739, 820, 734, 717, 834, 792, 811, 780, 831, 867, ..., .
(End)

Crossrefs

Programs

  • Mathematica
    f[n_] := f[n] = Count[ SquareFreeQ@# & /@ (n - Range[ Floor[ Sqrt[n]]]^2), True]; t = Array[ f, 10000]; Table[ Position[ t, n, 1, 1], {n, 0, 100}] (* Robert G. Wilson v, May 17 2014 *)

Extensions

Edited by N. J. A. Sloane, May 23 2014

A334671 Number of ways to write n as the sum of a squarefree number (A005117) and a square (A000290).

Original entry on oeis.org

1, 2, 2, 1, 2, 3, 3, 1, 1, 3, 4, 2, 1, 4, 4, 2, 3, 3, 4, 2, 3, 4, 5, 2, 1, 5, 4, 2, 2, 6, 5, 3, 3, 3, 6, 2, 4, 7, 7, 3, 3, 7, 5, 3, 2, 6, 7, 3, 2, 5, 7, 3, 3, 4, 7, 4, 4, 5, 7, 4, 2, 8, 5, 3, 4, 8, 7, 4, 5, 7, 9, 3, 4, 7, 7, 2, 5, 9, 6, 4, 3, 8, 10, 4, 3, 9, 10, 4, 4, 6
Offset: 1

Author

Michel Marcus, Oct 31 2020

Keywords

Comments

Differs from A085263 where the square cannot be zero.

Crossrefs

Cf. A000290, A005117, A085263 (with a positive square).

Programs

  • PARI
    a(n) = sum(k=0, n, issquare(k) * issquarefree(n-k));
Showing 1-5 of 5 results.