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 1-10 of 11 results. Next

A244630 a(n) = 17*n^2.

Original entry on oeis.org

0, 17, 68, 153, 272, 425, 612, 833, 1088, 1377, 1700, 2057, 2448, 2873, 3332, 3825, 4352, 4913, 5508, 6137, 6800, 7497, 8228, 8993, 9792, 10625, 11492, 12393, 13328, 14297, 15300, 16337, 17408, 18513, 19652, 20825, 22032, 23273, 24548, 25857, 27200, 28577, 29988
Offset: 0

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Author

Vincenzo Librandi, Jul 03 2014

Keywords

Comments

First bisection of A195047. - Bruno Berselli, Jul 03 2014
Norms of purely imaginary numbers in Z[sqrt(-17)] (for example, 3*sqrt(-17) has norm 153). - Alonso del Arte, Jun 23 2018

Crossrefs

Cf. similar sequences of the type k*n^2: A000290 (k = 1), A001105 (k = 2), A033428 (k = 3), A016742 (k = 4), A033429 (k = 5), A033581 (k = 6), A033582 (k = 7), A139098 (k = 8), A016766 (k = 9), A033583 (k = 10), A033584 (k = 11), A135453 (k = 12), A152742 (k = 13), A144555 (k = 14), A064761 (k = 15), A016802 (k = 16), this sequence (k = 17), A195321 (k = 18), A244631 (k = 19), A195322 (k = 20), A064762 (k = 21), A195323 (k = 22), A244632 (k = 23), A195824 (k = 24), A016850 (k = 25), A244633 (k = 26), A244634 (k = 27), A064763 (k = 28), A244635 (k = 29), A244636 (k = 30).

Programs

Formula

G.f.: 17*x*(1 + x)/(1 - x)^3. [corrected by Bruno Berselli, Jul 03 2014]
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 2.
a(n) = 17*A000290(n). - Omar E. Pol, Jul 03 2014
a(n) = a(-n). - Muniru A Asiru, Jun 29 2018
From Elmo R. Oliveira, Dec 02 2024: (Start)
E.g.f.: 17*x*(1 + x)*exp(x).
a(n) = n*A008599(n) = A195047(2*n). (End)

A016910 a(n) = (6*n)^2.

Original entry on oeis.org

0, 36, 144, 324, 576, 900, 1296, 1764, 2304, 2916, 3600, 4356, 5184, 6084, 7056, 8100, 9216, 10404, 11664, 12996, 14400, 15876, 17424, 19044, 20736, 22500, 24336, 26244, 28224, 30276, 32400, 34596, 36864, 39204, 41616, 44100, 46656, 49284, 51984, 54756, 57600, 60516, 63504, 66564, 69696, 72900
Offset: 0

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Author

Keywords

Comments

Areas A of two classes of triangles with integer sides (a,b,c) where a = 9k, b=10k and c = 17k, or a = 3k, b = 25k and c = 26k for k=0,1,2,... These areas are given by Heron's formula A = sqrt(s(s-a)(s-b)(s-c)) = (6k)^2, with the semiperimeter s = (a+b+c)/2. This sequence is a subsequence of A188158. - Michel Lagneau, Oct 11 2013
Sequence found by reading the line from 0, in the direction 0, 36, ..., in the square spiral whose vertices are the generalized 20-gonal numbers A218864. - Omar E. Pol, May 13 2018.

Crossrefs

Cf. similar sequences of the type k*n^2: A000290 (k=1), A001105 (k=2), A033428 (k=3), A016742 (k=4), A033429 (k=5), A033581 (k=6), A033582 (k=7), A139098 (k=8), A016766 (k=9), A033583 (k=10), A033584 (k=11), A135453 (k=12), A152742 (k=13), A144555 (k=14), A064761 (k=15), A016802 (k=16), A244630 (k=17), A195321 (k=18), A244631 (k=19), A195322 (k=20), A064762 (k=21), A195323 (k=22), A244632 (k=23), A195824 (k=24), A016850 (k=25), A244633 (k=26), A244634 (k=27), A064763 (k=28), A244635 (k=29), A244636 (k=30).

Programs

Formula

From Ilya Gutkovskiy, Jun 09 2016: (Start)
O.g.f.: 36*x*(1 + x)/(1 - x)^3.
E.g.f.: 36*x*(1 + x)*exp(x).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
Sum_{n>=1} 1/a(n) = Pi^2/216 = A086726. (End)
Product_{n>=1} a(n)/A136017(n) = Pi/3. - Fred Daniel Kline, Jun 09 2016
a(n) = t(9*n) - 9*t(n), where t(i) = i*(i+k)/2 for any k. Special case (k=1): a(n) = A000217(9*n) - 9*A000217(n). - Bruno Berselli, Aug 31 2017
a(n) = 36*A000290(n) = 18*A001105(n) = 12*A033428 = 9*A016742(n) = 6*A033581(n) = 4*A016766(n) = 3*A135453(n) = 2*A195321(n). - Omar E. Pol, Jun 07 2018
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi^2/432. - Amiram Eldar, Jun 27 2020
From Amiram Eldar, Jan 25 2021: (Start)
Product_{n>=1} (1 + 1/a(n)) = sinh(Pi/6)/(Pi/6).
Product_{n>=1} (1 - 1/a(n)) = sin(Pi/6)/(Pi/6) = 3/Pi (A089491). (End)

A017222 a(n) = (9*n + 5)^2.

Original entry on oeis.org

25, 196, 529, 1024, 1681, 2500, 3481, 4624, 5929, 7396, 9025, 10816, 12769, 14884, 17161, 19600, 22201, 24964, 27889, 30976, 34225, 37636, 41209, 44944, 48841, 52900, 57121, 61504, 66049, 70756
Offset: 0

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Author

Keywords

Crossrefs

Sequences of the form (m*n+5)^2: A010864 (m=0), A000290 (m=1), A016754 (m=2), A016790 (m=3), A016814 (m=4), A016850 (m=5), A016970 (m=6), A017042 (m=7), A017126 (m=8), this sequence (m=9), A017330 (m=10), A017450 (m=11), A017582 (m=12).

Programs

Formula

a(n) = A017221(n)^2.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Harvey P. Dale, May 22 2012
G.f.: (25 + 121*x + 16*x^2)/(1-x)^3. - R. J. Mathar, Mar 20 2018
From G. C. Greubel, Dec 29 2022: (Start)
a(2*n+1) = 4*A017246(n).
a(n) = a(n-1) + 9*(18*n + 1).
E.g.f.: (25 + 171*x + 81*x^2)*exp(x). (End)

A017270 a(n) = (10*n)^2.

Original entry on oeis.org

0, 100, 400, 900, 1600, 2500, 3600, 4900, 6400, 8100, 10000, 12100, 14400, 16900, 19600, 22500, 25600, 28900, 32400, 36100, 40000, 44100, 48400, 52900, 57600, 62500, 67600, 72900, 78400, 84100, 90000, 96100, 102400, 108900, 115600, 122500, 129600, 136900, 144400
Offset: 0

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Author

Keywords

Crossrefs

Programs

Formula

a(n) = a(n-1) + 200*n - 100, n > 0 ; a(0)=0. - Miquel Cerda, Oct 30 2016
G.f.: 100*x*(1 + x)/(1 - x)^3. - Ilya Gutkovskiy, Oct 30 2016
a(n) = 100*A000290(n). - Michel Marcus, Oct 30 2016
From Amiram Eldar, Jan 25 2021: (Start)
Sum_{n>=1} 1/a(n) = Pi^2/600.
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi^2/1200.
Product_{n>=1} (1 + 1/a(n)) = sinh(Pi/10)/(Pi/10).
Product_{n>=1} (1 - 1/a(n)) = sin(Pi/10)/(Pi/10) = 5*(sqrt(5)-1)/(2*Pi). (End)
From Elmo R. Oliveira, Nov 30 2024: (Start)
E.g.f.: 100*x*(1 + x)*exp(x).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 2.
a(n) = A008592(n)^2 = A000290(A008592(n)) = A016850(2*n). (End)

A016898 a(n) = (5*n + 4)^2.

Original entry on oeis.org

16, 81, 196, 361, 576, 841, 1156, 1521, 1936, 2401, 2916, 3481, 4096, 4761, 5476, 6241, 7056, 7921, 8836, 9801, 10816, 11881, 12996, 14161, 15376, 16641, 17956, 19321, 20736, 22201, 23716, 25281, 26896, 28561, 30276, 32041, 33856, 35721, 37636, 39601, 41616
Offset: 0

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Author

Keywords

Comments

If Y is a fixed 2-subset of a (5n+1)-set X then a(n-1) is the number of 3-subsets of X intersecting Y. - Milan Janjic, Oct 21 2007
Interleaving of A017318 and A017378. - Michel Marcus, Aug 26 2015

Examples

			a(0) = (5*0 + 4)^2 = 16.
		

Crossrefs

Programs

  • Magma
    [(5*n+4)^2: n in [0..70]]; // Vincenzo Librandi, May 02 2011
    
  • Mathematica
    Table[(5*n + 4)^2, {n, 0, 25}] (* Amiram Eldar, Oct 02 2020 *)
    LinearRecurrence[{3,-3,1},{16,81,196},50] (* Harvey P. Dale, Jul 30 2023 *)
  • PARI
    Vec((16 + 33*x + x^2) / (1 - x)^3 + O(x^40)) \\ Colin Barker, Mar 30 2017

Formula

From Colin Barker, Mar 30 2017: (Start)
G.f.: (16 + 33*x + x^2) / (1 - x)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>2.
(End)
Sum_{n>=0} 1/a(n) = polygamma(1, 4/5)/25. - Amiram Eldar, Oct 02 2020

A156701 a(n) = 4*n^4 + 17*n^2 + 4.

Original entry on oeis.org

4, 25, 136, 481, 1300, 2929, 5800, 10441, 17476, 27625, 41704, 60625, 85396, 117121, 157000, 206329, 266500, 339001, 425416, 527425, 646804, 785425, 945256, 1128361, 1336900, 1573129, 1839400, 2138161, 2471956, 2843425, 3255304, 3710425
Offset: 0

Views

Author

Reinhard Zumkeller, Feb 13 2009

Keywords

Comments

a(n) = A087475(n)*A053755(n).

Crossrefs

Programs

  • Magma
    [4*n^4+17*n^2+4: n in [0..50]]; // Vincenzo Librandi, Dec 27 2010
    
  • Mathematica
    Table[4n^4+17n^2+4,{n,0,40}] (* or *) LinearRecurrence[{5,-10,10,-5,1},{4,25,136,481,1300},50] (* Harvey P. Dale, Nov 08 2017 *)
  • PARI
    a(n)=4*n^4+17*n^2+4 \\ Charles R Greathouse IV, Oct 21 2022

Formula

a(n) = (2*(n^2 - 1))^2 + (5*n)^2.
G.f.: (-4-25*x^4-11*x^3-51*x^2-5*x)/(x-1)^5. - Maksym Voznyy (voznyy(AT)mail.ru), Jul 26 2009
E.g.f.: exp(x)*(4 + 21*x + 45*x^2 + 24*x^3 + 4*x^4). - Stefano Spezia, Jul 08 2023

A010015 a(0) = 1, a(n) = 25*n^2 + 2 for n > 0.

Original entry on oeis.org

1, 27, 102, 227, 402, 627, 902, 1227, 1602, 2027, 2502, 3027, 3602, 4227, 4902, 5627, 6402, 7227, 8102, 9027, 10002, 11027, 12102, 13227, 14402, 15627, 16902, 18227, 19602, 21027, 22502, 24027, 25602, 27227, 28902, 30627, 32402, 34227, 36102, 38027, 40002
Offset: 0

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Author

Keywords

Comments

Subsequence of A160842. - Bruno Berselli, Feb 06 2012
The identity (25*n^2 + 1)^2 - (25*n^2 + 2)*(5*n)^2 = 1 can be written as (A016850(n+1) + 1)^2 - a(n+1)*A008587(n+1)^2 = 1. - Vincenzo Librandi, Feb 08 2012

Crossrefs

Cf. A206399.

Programs

Formula

G.f.: (1+x)*(1 + 23*x + x^2)/(1-x)^3. - Bruno Berselli, Feb 06 2012
E.g.f.: (x*(x+1)*25 + 2)*e^x - 1. - Gopinath A. R., Feb 14 2012
Sum_{n>=0} 1/a(n) =3/4+sqrt(2)/20*Pi*coth(Pi*sqrt(2)/5) = 1.062575323280590.. - R. J. Mathar, May 07 2024
a(n) = A262221(n)+A262221(n+1). - R. J. Mathar, May 07 2024

A133496 a(n) = (29*n)^2.

Original entry on oeis.org

0, 841, 3364, 7569, 13456, 21025, 30276, 41209, 53824, 68121, 84100, 101761, 121104, 142129, 164836, 189225, 215296, 243049, 272484, 303601, 336400, 370881, 407044, 444889, 484416, 525625, 568516, 613089, 659344, 707281, 756900, 808201
Offset: 0

Views

Author

Richard Choulet, Dec 23 2007

Keywords

Examples

			a(1) = 29^2 = 841, a(2) = 58^2 = 3364, a(3) = 87^2 = 7569.
		

Crossrefs

Cf. A016850.

Programs

Formula

G.f.: -841*x*(1+x) / (x-1)^3 . - R. J. Mathar, Mar 13 2015

Extensions

More terms from Philippe Deléham, Dec 21 2008
a(12) corrected by Vincenzo Librandi, Apr 26 2011

A232329 Integer areas A of the integer-sided triangles such that the product of the inradius and the circumradius is a square.

Original entry on oeis.org

42, 168, 378, 672, 1050, 1512, 2058, 2088, 2688, 3000, 3402, 4200, 5082, 6048, 6960, 7098, 8232, 8352, 9450, 10752, 12000, 12138, 13608, 15162, 16800, 18522, 18792, 20328, 22218, 24192, 26250, 27000, 27840, 28392, 30618, 31416, 32928, 33408, 35322, 36000, 37800, 40362
Offset: 1

Views

Author

Michel Lagneau, Nov 22 2013

Keywords

Comments

The areas of the primitive triangles of sides (a, b, c) and inradius, circumradius equals respectively to r and R are 42, 3000,... The sides of the nonprimitive triangles are of the form (a*k, b*k, c*k) with r’ = r*k and R’=R*k where r’, R’ are respectively the inradius and the circumradius of the nonprimitive triangles. The areas A’ of the nonprimitive triangles are A’ = A*k^2. The set {A016850} (numbers (5n)^2) is included in the set of the products r*R (see the table below).
The area A of a triangle whose sides have lengths a, b, and c is given by Heron's formula: A = sqrt(s*(s-a)*(s-b)*(s-c)), where s = (a+b+c)/2. The inradius r is given by r = A/s and the circumradius is given by R = abc/4A.
The product r*R is given by r*R = abc/2(a+b+c).
The following table gives the first values (A, a, b, c, r, R, r*R).
-----------------------------------------------------
| A | a | b | c | r | R | r*R |
-----------------------------------------------------
| 42 | 7 | 15 | 20 | 2 | 25/2 | 5^2 |
| 168 | 14 | 30 | 40 | 4 | 25 | 10^2 |
| 378 | 21 | 45 | 60 | 6 | 75/2 | 15^2 |
| 672 | 28 | 60 | 80 | 8 | 50 | 20^2 |
| 1050 | 35 | 75 | 100 | 10 | 125/2 | 25^2 |
| 1512 | 42 | 90 | 120 | 12 | 75 | 30^2 |
| 2058 | 49 | 105 | 140 | 14 | 175/2 | 35^2 |
| 2688 | 56 | 120 | 160 | 16 | 100 | 40^2 |
| 3000 | 80 | 85 | 85 | 24 | 289/6 | 34^2 |
| 3402 | 63 | 135 | 180 | 18 | 225/2 | 45^2 |
| 4200 | 70 | 150 | 200 | 20 | 125 | 50^2 |
| 5082 | 77 | 165 | 220 | 22 | 275/2 | 55^2 |
| 6048 | 84 | 180 | 240 | 24 | 150 | 60^2 |
| 6960 | 58 | 300 | 338 | 20 | 845/4 | 65^2 |
| 7098 | 91 | 195 | 260 | 26 | 325/2 | 65^2 |
....................................................

Examples

			a(1) = 42 because, for (a,b,c) = (7, 15, 20):
  the semiperimeter s = (7+15+20)/2 =21, and
  A = sqrt(21*(21-7)*(21-15)*(21-20)) = 42
  R = abc/4A = 7*15*20/(4*42) = 25/2
  r = A/s = 42/21 = 2, hence r*R = 25 is a square.
		

References

  • Mohammad K. Azarian, Circumradius and Inradius, Problem S125, Math Horizons, Vol. 15, Issue 4, April 2008, p. 32.

Crossrefs

Programs

  • Mathematica
    nn=800;lst={};Do[s=(a+b+c)/2;rr=a*b*c/(2*(a+b+c))
    ;If[IntegerQ[s],area2=s(s-a)(s-b)(s-c);If[0
    				
  • PARI
    lista(nn)=lst=[]; for (a = 1, nn, for (b=1, a, for (c=1, b, s=(a+b+c)/2; rr=a*b*c/(2*(a+b+c)); if ((type(s) == "t_INT") && (type(rr) == "t_INT"), area2=s*(s-a)*(s-b)*(s-c); if ((0Michel Marcus, Jun 09 2015
    
  • PARI
    {for(a=20,10000,forstep(b=a,2,-1,forstep(c=min(b,a+b-1),a-b+1,-1,if((a+b+c)%2<1,s=(a+b+c)/2;if(issquare(s*(s-a)*(s-b)*(s-c),&A),
    if((a*b*c)%(2*(a+b+c))<1&&if(issquare(a*b*c/(2*(a+b+c)),&d),
    print([A,a,b,c,s,d]))))))))} \\ Faster version used for afile. Zak Seidov, Jun 06 2015

Extensions

Missing term 33408 added by Zak Seidov, Jun 08 2015

A303302 a(n) = 34*n^2.

Original entry on oeis.org

0, 34, 136, 306, 544, 850, 1224, 1666, 2176, 2754, 3400, 4114, 4896, 5746, 6664, 7650, 8704, 9826, 11016, 12274, 13600, 14994, 16456, 17986, 19584, 21250, 22984, 24786, 26656, 28594, 30600, 32674, 34816, 37026, 39304, 41650, 44064, 46546, 49096, 51714, 54400, 57154, 59976, 62866, 65824, 68850, 71944
Offset: 0

Views

Author

Omar E. Pol, May 13 2018

Keywords

Comments

Sequence found by reading the line from 0, in the direction 0, 34, ..., in the square spiral whose vertices are the generalized 19-gonal numbers A303813.

Crossrefs

Cf. similar sequences of the type k*n^2: A000290 (k=1), A001105 (k=2), A033428 (k=3), A016742 (k=4), A033429 (k=5), A033581 (k=6), A033582 (k=7), A139098 (k=8), A016766 (k=9), A033583 (k=10), A033584 (k=11), A135453 (k=12), A152742 (k=13), A144555 (k=14), A064761 (k=15), A016802 (k=16), A244630 (k=17), A195321 (k=18), A244631 (k=19), A195322 (k=20), A064762 (k=21), A195323 (k=22), A244632 (k=23), A195824 (k=24), A016850 (k=25), A244633 (k=26), A244634 (k=27), A064763 (k=28), A244635 (k=29), A244636 (k=30), A244082 (k=32), this sequence (k=34), A016910 (k=36), A016982 (k=49), A017066 (k=64), A017162 (k=81), A017270 (k=100), A017390 (k=121), A017522 (k=144).

Programs

  • Magma
    [34*n^2: n in [0..50]]; // Vincenzo Librandi Jun 07 2018
  • Mathematica
    Table[34 n^2, {n, 0, 40}]
    LinearRecurrence[{3,-3,1},{0,34,136},50] (* Harvey P. Dale, Jul 23 2018 *)
  • PARI
    a(n) = 34*n^2;
    
  • PARI
    concat(0, Vec(34*x*(1 + x) / (1 - x)^3 + O(x^40))) \\ Colin Barker, Jun 12 2018
    

Formula

a(n) = 34*A000290(n) = 17*A001105(n) = 2*A244630(n).
G.f.: 34*x*(1 + x)/(1 - x)^3. - Vincenzo Librandi, Jun 07 2018
From Elmo R. Oliveira, Dec 02 2024: (Start)
E.g.f.: 34*x*(1 + x)*exp(x).
a(n) = A005843(n)*A008599(n).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 2. (End)
Showing 1-10 of 11 results. Next