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.

Previous Showing 11-19 of 19 results.

A214329 Complement of A214328.

Original entry on oeis.org

2, 3, 5, 6, 8, 9, 10, 11, 12, 13, 14, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 29, 30, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50, 51, 52, 53, 54, 56, 57, 58, 59, 61, 62, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 85, 86, 88, 89, 90, 91, 93, 94, 96, 97, 98, 99, 100, 101, 102, 104, 105, 106, 107, 108, 109
Offset: 1

Views

Author

N. J. A. Sloane, Jul 26 2012, following a suggestion from Hans Isdahl, Apr 19 2012

Keywords

Comments

Numbers that are the sum of 2 or 3 nonzero squares. - Altug Alkan, Jan 13 2016

Crossrefs

Programs

  • PARI
    is2(n) = {for( i=1, #n=factor(n)~%4, n[1, i]==3 && n[2, i]%2 && return); n && ( vecmin(n[1, ])==1 || (n[1, 1]==2 && n[2, 1]%2))}
    is3(n) = {my(a, b) ; a=1; while(a^2+1Altug Alkan, Jan 13 2016

A267189 (Cubes of positive numbers) that are not the sum of three nonzero squares.

Original entry on oeis.org

1, 8, 64, 343, 512, 3375, 4096, 12167, 21952, 29791, 32768, 59319, 103823, 166375, 216000, 250047, 262144, 357911, 493039, 658503, 778688, 857375, 1092727, 1367631, 1404928, 1685159, 1906624, 2048383, 2097152, 2460375, 2924207, 3442951, 3796416, 4019679, 4657463, 5359375, 6128487
Offset: 1

Views

Author

N. J. A. Sloane, Jan 18 2016

Keywords

Comments

This is the intersection of A004214 and A000578.
The original definition of A134739 was ambiguous - this is the second way it could have been interpreted. The other way, now the official definition of A134739, being "Cubes of (positive numbers that are not the sum of three nonzero squares)".

Crossrefs

Programs

  • PARI
    is(n) = { my(a, b) ; a=1; while(a^2+1Altug Alkan, Jan 18 2016

Extensions

More terms from Altug Alkan, Jan 18 2016

A125112 Numbers which are not the sum of 3 nonzero squares, but which can be expressed as the product of two numbers that are the sum of 3 nonzero squares.

Original entry on oeis.org

63, 87, 135, 156, 159, 183, 207, 231, 252, 279, 303, 319, 327, 348, 351, 375, 399, 423, 444, 447, 471, 476, 495, 519, 540, 543, 551, 567, 572, 583, 591, 615, 624, 636, 639, 663, 671, 687, 700, 711, 732, 735, 759, 783, 807, 828, 831, 847, 855, 879, 903, 924
Offset: 1

Views

Author

Artur Jasinski, Nov 21 2006

Keywords

Comments

Intersection of A004214 with products of pairs of terms of A000408.

Examples

			a(2) = 87 = 3 * 29 = (1^2+1^2+1^2) * (4^2+3^2+2^2)
87 does not have a partition as a sum x^2+y^2+z^2 with x,y,z>0
63=3*21; 87=3*29; 135=3*45; 156=6*26; 572=22*26;
		

Crossrefs

Cf. A000408 (sums of 3 nonzero squares), A004214 (not sums of 3 nonzero squares).

Programs

  • Maple
    isA000408 := proc(n) local a,b,c2 ; a:=1; while a^2A125112 := proc(n) local d,i; if isA000408(n) then RETURN(false) ; else d := numtheory[divisors](n) ; for i from 1 to nops(d) do if isA000408(op(i,d)) and isA000408(n/op(i,d)) then RETURN(true) ; fi ; od ; RETURN(false) ; fi ; end: for an from 1 to 1600 do if isA125112(an) then printf("%d,",an) ; fi ; od ; # R. J. Mathar, Nov 23 2006
  • Mathematica
    isA000408[n_] := Module[{a, b, c2}, a = 1; While[a^2 < n, b = 1; While[b <= a && a^2 + b^2 < n, c2 = n - a^2 - b^2; If[IntegerQ@Sqrt@c2, Return[True]]; b++]; a++]; Return[False]];
    isA125112[n_] := Module[{d, i}, If[isA000408[n], Return[False], d = Divisors[n]; For[i = 1, i <= Length[d], i++, If[isA000408[d[[i]]] && isA000408[n/d[[i]]], Return[True]]]; Return[False]]];
    Select[Range[1600], isA125112] (* Jean-François Alcover, Jul 22 2024, after R. J. Mathar *)

Extensions

Edited and extended by R. J. Mathar and Ray Chandler, Nov 23 2006

A178615 Smaller of two consecutive numbers that are not the sum of 3 nonzero squares.

Original entry on oeis.org

1, 4, 7, 15, 31, 39, 63, 79, 111, 127, 159, 207, 231, 239, 255, 319, 367, 399, 447, 495, 511, 519, 591, 623, 639, 751, 831, 879, 927, 959, 1007, 1023, 1135, 1263, 1279, 1359, 1391, 1471, 1519, 1599, 1647, 1775, 1791, 1903, 1983, 2031, 2047, 2079, 2159, 2287
Offset: 1

Views

Author

Keywords

Comments

{1,2,4,5,7,8,10,13,15,16,20,23,25,28,31,32,..}->{1,4,7,15,31,..}

Crossrefs

Programs

  • Mathematica
    q=66;q2=q^2+2;lst={};Do[Do[Do[z=a^2+b^2+c^2;If[z<=q2,AppendTo[lst,z]],{c,b,1,-1}],{b,a,1,-1}],{a,q}];lst; u=Union@lst;a=Complement[Range[q^2],u];lst={};Do[If[a[[n+1]]-a[[n]]==1,AppendTo[lst,a[[n]]]],{n,Length[a]-1}];lst

A180917 Numbers that are not the sum of three positive heptagonal numbers.

Original entry on oeis.org

1, 2, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 16, 17, 18, 19, 22, 23, 24, 25, 27, 28, 29, 30, 31, 33, 34, 35, 38, 39, 40, 41, 44, 45, 46, 47, 49, 50, 51, 52, 55, 56, 58, 60, 61, 62, 64, 65, 66, 67, 68, 71, 72, 73, 76, 77, 78, 79, 81, 82, 84, 85, 87, 88, 92, 93, 94, 97, 98, 99, 101
Offset: 1

Views

Author

Jonathan Vos Post, Sep 23 2010

Keywords

Comments

Complement of A117105. This is to heptagonal numbers A000566,
as A007536 is to hexagonal numbers A000384,
as A003679 is to pentagonal numbers A000326,
and as A004214 is to squares A000290.
This sequence is presumably finite: what is its likely last element?
Last element appears to be a(1671) = 273118. - Charles R Greathouse IV, Sep 27 2010

Crossrefs

A330708 Numbers that are not the sum of 2 nonzero squares and a positive cube.

Original entry on oeis.org

0, 1, 2, 4, 5, 7, 8, 12, 15, 17, 20, 22, 23, 24, 31, 36, 39, 43, 50, 55, 57, 63, 65, 70, 71, 78, 87, 94, 103, 111, 113, 115, 119, 120, 134, 139, 141, 148, 160, 167, 169, 185, 204, 211, 254, 263, 267, 279, 283, 286, 302, 311, 312, 331, 335, 342, 349, 379, 391
Offset: 1

Views

Author

XU Pingya, Jun 08 2020

Keywords

Comments

A022552 is a subsequence.
a(490) = A022552(434) = 5042631. No more terms <= 4 * 10^7.

Crossrefs

Programs

  • Maple
    N:= 500: # for terms <= N
    G1:= add(x^(i^2), i=1..floor(sqrt(N))):
    G2:= add(x^(i^3), i=1..floor(N^(1/3))):
    G:= expand(G1^2*G2):
    select(t -> coeff(G,x,t)=0, [$0..N]); # Robert Israel, Jun 12 2020
  • Mathematica
    m = 0;
    n = 400.;
    t = Union@Flatten@Table[x^2 + y^2 + z^3, {x, (n/2)^(1/2)}, {y, x, (n - x^2)^(1/2)}, {z, If[x^2 + y^2 < m, Floor[(m - 1 - x^2 - y^2)^(1/3)] + 1, 1], (n - x^2 - y^2)^(1/3)}];
    Complement[Range[m, n], t]

A273123 Values of A007692(n) that are not of the form x^2 + y^2 + z^2 where x, y, z are nonzero integers.

Original entry on oeis.org

85, 130, 340, 520, 1360, 2080, 5440, 8320, 21760, 33280, 87040, 133120, 348160, 532480, 1392640, 2129920, 5570560, 8519680, 22282240, 34078720, 89128960, 136314880, 356515840, 545259520, 1426063360, 2181038080, 5704253440, 8724152320
Offset: 1

Views

Author

Altug Alkan, May 16 2016

Keywords

Comments

If n is in this sequence, then 4*n is also in this sequence. So 85*4^k and 130*4^k are terms of this sequence for all nonnegative values of k.
For more details see A051952.

Examples

			85 is a term because 85 = 2^2 + 9^2 = 6^2 + 7^2 and 85 = x^2 + y^2 + z^2 has no solution for nonzero integer values of x, y, z.
130 is a term because 130 = 3^2 + 11^2 = 7^2 + 9^2 and 130 = x^2 + y^2 + z^2 has no solution for nonzero integer values of x, y, z.
340 is a term because 340 = 4*85 and 85 is a term.
		

Crossrefs

Programs

  • Mathematica
    twoQ[n_] := 2 == Length@ Select[ PowersRepresentations[n, 2, 2], Times @@ # > 0 &, 2]; threeQ[n_] := {} != Quiet@ IntegerPartitions[n, {3}, Range[ Sqrt@ n]^2, 1]; Select[Range[10^5], twoQ[#] && ! threeQ[#] &] (* Giovanni Resta, May 16 2016 *)

Extensions

a(14)-a(28) from Giovanni Resta, May 16 2016

A335658 Numbers that are not the sum of 3 nonzero squares and a positive cube.

Original entry on oeis.org

0, 1, 2, 3, 5, 6, 8, 9, 16, 21, 24, 40
Offset: 1

Views

Author

XU Pingya, Jun 17 2020

Keywords

Comments

No more terms up to 6*10^5.

Crossrefs

Programs

  • Mathematica
    n = 5 * 10^4.;
    t = Union@Flatten@Table[x^2 + y^2 + z^2 + w^3, {x,(n/3)^(1/2)}, {y,x,((n-x^2)/2)^(1/2)},{z,y,(n-x^2-y^2)^(1/2)}, {w,(n-x^2-y^2-z^2)^(1/3)}];
    Complement[Range[0,n],t]

A335659 Numbers that are not the sum of 3 nonzero squares and a positive 5th power.

Original entry on oeis.org

0, 1, 2, 3, 5, 6, 8, 9, 11, 14, 16, 17, 21, 24, 26, 29, 32, 33, 40, 48, 64, 72, 96, 112, 144, 160, 192, 240
Offset: 1

Views

Author

XU Pingya, Jun 17 2020

Keywords

Comments

No more terms up to 10^6.

Crossrefs

Programs

  • Mathematica
    n = 10^5;
    t = Union@Flatten@Table[x^2 + y^2 + z^2 + w^5, {x, (n/3)^(1/2)}, {y, x, ((n-x^2)/2)^(1/2)}, {z, y, (n-x^2-y^2)^(1/2)}, {w, 1, (n-x^2-y^2-z^2)^(1/5)}];
    Complement[Range[0, n], t]
Previous Showing 11-19 of 19 results.