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 1-4 of 4 results.

A292313 Numbers that are the sum of three squares in arithmetic progression.

Original entry on oeis.org

75, 300, 507, 675, 867, 1200, 1875, 2028, 2523, 2700, 3468, 3675, 4107, 4563, 4800, 5043, 6075, 7500, 7803, 8112, 8427, 9075, 10092, 10800, 11163, 12675, 13872, 14700, 15987, 16428, 16875, 18252, 19200, 20172, 21675, 22707, 23763, 24300, 24843, 27075, 28227, 30000, 30603
Offset: 1

Views

Author

Antonio Roldán, Sep 14 2017

Keywords

Examples

			75 = 1^2 + 5^2 + 7^2 = 1 + 25 + 49, with 25 - 1 = 49 - 25 = 24.
675 = 3^2 + 15^2 + 21^2 = 9 + 225 + 441, with 225 - 9 = 441 - 225 = 216.

Links

Crossrefs

Subsequence of A033428.
Cf. A000290, A000378, A004431, A134422, A292309, A292310, A292314, A292316.

Programs

  • PARI
    t=4; k=3; while(t<=13000, i=k; e=0; v=t+i; while(i>1&&e==0, if(issquare(v), m=3*t; e=1; print1(m,", ")); i+=-2; v+=i); k+=2; t+=k)

Formula

Sequence is 3*(distinct elements in A198385).
Numbers of the form 3*m^2 where 2*m^2 is in A004431. - Chai Wah Wu, Oct 05 2017

A292309 Numbers equal to the sum of three triangular numbers in arithmetic progression.

Original entry on oeis.org

9, 63, 84, 108, 234, 315, 459, 513, 570, 630, 759, 975, 1053, 1134, 1395, 1584, 1998, 2109, 2709, 2838, 2970, 3105, 3384, 3528, 3825, 4134, 4455, 4620, 4788, 4959, 5133, 5310, 5673, 5859, 6834, 7038, 7668, 7884, 8325, 8778, 9009, 9243, 9480, 10209, 10710, 11223
Offset: 1

Views

Author

Antonio Roldán, Sep 14 2017

Keywords

Comments

Subsequence of A045943, because a(n) = 3*k*(k+1)/2 = 3*A000217(k) for some k.

Examples

			9 = A000217(0) + A000217(2) + A000217(3) = 0 + 3 + 6, with 6 - 3 = 3 - 0 = 3.
513 = A000217(11) + A000217(18) + A000217(23) = 66 + 171 + 276, with 171 - 66 = 276 - 171 = 105.

Crossrefs

Cf. A000217, A045943, A127329, A292310, A292313, A292314, A292316.

Programs

  • Mathematica
    Module[{t = 3, k = 2, i, e, v, m}, Reap[While[t <= 5000, i = k; e = 0; v = t+i; While[i > 0 && e == 0, If[IntegerQ @ Sqrt[8v+1], m = 3t; e = 1; Sow[m]]; i--; v += i]; k++; t += k]][[2, 1]]] (* Jean-François Alcover, Jun 25 2023, after PARI code *)
  • PARI
    t=3;k=2;while(t<=5000,i=k;e=0;v=t+i;while(i>1&&e==0,if(issquare(8*v+1),m=3*t;e=1;print1(m,", "));i+=-1;v+=i);k+=1;t+=k)

Formula

a(n) = 3*A292310(n).

A292314 Numbers equal to the sum of three oblong numbers in arithmetic progression.

Original entry on oeis.org

18, 126, 168, 216, 468, 918, 1026, 1140, 1260, 1518, 1950, 2106, 2268, 2790, 3168, 3996, 4218, 5418, 5676, 5940, 6210, 6768, 7056, 7650, 8268, 8910, 9240, 9576, 9918, 10266, 10620, 11346, 11718, 13668, 14076, 15336, 15768, 16650, 17556, 18018, 18486, 18960, 20418, 21420, 22446
Offset: 1

Views

Author

Antonio Roldán, Sep 14 2017

Keywords

Comments

Subsequence of A028896.

Examples

			126 = 3*4 + 6*7 + 8*9 = 12 + 42 + 72, with 72 - 42 = 42 - 12 = 30;
468 = 8*9 + 12*13 + 15*16 = 72 + 156 + 240, with 240 - 156 = 156 - 72 = 84.

Crossrefs

Cf. A292309, A292310, A292313, A292316.

Programs

  • Mathematica
    o[n_] := n(n+1); s[x_] := Reduce[ x+k == o[y] && x-k == o[z] && k>0 && z>0, {z, y, k}, Integers]; 3 Select[o@ Range@ 93, s[#] =!= False &] (* Giovanni Resta, Sep 18 2017 *)
  • PARI
    t=2; k=2; while(t<=10^4, i=k; e=0; v=t+i; while(i>2&&e==0, if(issquare(4*v+1), m=3*t; e=1; print1(m,", ")); i+=-2; v+=i); k+=2; t+=k)

Formula

a(n) = 3*A292316(n).

A292316 Oblong numbers equidistant from two other oblong numbers.

Original entry on oeis.org

6, 42, 56, 72, 156, 306, 342, 380, 420, 506, 650, 702, 756, 930, 1056, 1332, 1406, 1806, 1892, 1980, 2070, 2256, 2352, 2550, 2756, 2970, 3080, 3192, 3306, 3422, 3540, 3782, 3906, 4556, 4692, 5112, 5256, 5550, 5852, 6006, 6162, 6320, 6806, 7140, 7482, 7656, 8190, 8372, 8556, 8742
Offset: 1

Views

Author

Antonio Roldán, Sep 14 2017

Keywords

Comments

Oblong numbers (A002378) that are the arithmetic mean of two other oblong numbers. - R. J. Mathar, Oct 05 2017

Examples

			6 = 2*3 is an oblong number and equidistant from 12 = 3*4 and 0 = 0*1.
342 = 18*19 is oblong number and equidistant from 132 = 11*12 and 552 = 23*24 (552-342 = 210; 342-132 = 210).

Crossrefs

Cf. A002378, A292309, A292310, A292313, A292314.

Programs

  • Mathematica
    o[n_] := n(n+1); s[x_] := Reduce[ x+k == o[y] && x-k == o[z] && k>0 && z>0, {z, y, k}, Integers]; Select[o@ Range@ 93, s[#] =!= False &] (* Giovanni Resta, Sep 18 2017 *)
  • PARI
    t=2;k=2;while(t<=10^4,i=k;e=0;v=t+i;while(i>2&&e==0,if(issquare(4*v+1),e=1;print1(t,", "));i+=-2;v+=i);k+=2;t+=k)

Formula

a(n) = A292314(n)/3.
Showing 1-4 of 4 results.

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