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.

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A017282 a(n) = (10*n + 1)^2.

Original entry on oeis.org

1, 121, 441, 961, 1681, 2601, 3721, 5041, 6561, 8281, 10201, 12321, 14641, 17161, 19881, 22801, 25921, 29241, 32761, 36481, 40401, 44521, 48841, 53361, 58081, 63001, 68121, 73441, 78961, 84681, 90601, 96721, 103041, 109561, 116281, 123201
Offset: 0

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Author

Keywords

Crossrefs

Sequences of the form (m*n+1)^2: A000012 (m=0), A000290 (m=1), A016754 (m=2), A016778 (m=3), A016814 (m=4), A016862 (m=5), A016922 (m=6), A016994 (m=7), A017078 (m=8), A017174 (m=9), this sequence (m=10), A017402 (m=11), A017534 (m=12), A134934 (m=14).
Cf. A017281.

Programs

  • Magma
    [(10*n+1)^2: n in [0..35]]; // Vincenzo Librandi, Jul 30 2011
    
  • Mathematica
    (* Programs from Michael De Vlieger, Mar 30 2017 *)
    Table[(10 n+1)^2, {n, 0, 35}]
    FoldList[#1 + 200 #2 - 80 &, 1, Range@ 35]
    CoefficientList[Series[(1+118x+81x^2)/(1-x)^3, {x,0,35}], x] (* End *)
    LinearRecurrence[{3,-3,1},{1,121,441},40] (* Harvey P. Dale, Sep 21 2017 *)
  • PARI
    for(n=0, 35, print1((10*n+1)^2", ")); \\ Bruno Berselli, Jul 30 2011
    
  • SageMath
    [(10*n+1)^2 for n in range(51)] # G. C. Greubel, Dec 24 2022

Formula

G.f.: (1+118*x+81*x^2)/(1-x)^3. - Bruno Berselli, Jul 30 2011
a(n) = a(n-1) + 40*(5*n-2), n > 0; a(0)=1. - Miquel Cerda, Oct 30 2016
a(n) = A017281(n)^2. - Michel Marcus, Oct 30 2016
E.g.f.: (1 +120*x +100*x^2)*exp(x). - G. C. Greubel, Dec 24 2022

Extensions

More terms from Bruno Berselli, Jul 30 2011

A350000 Table read by antidiagonals: T(n,k) (n >= 3, k >= 0) is the number of cells in a regular n-gon after k generations of mitosis.

Original entry on oeis.org

1, 1, 1, 1, 4, 1, 1, 4, 11, 1, 1, 4, 21, 24, 1, 1, 4, 31, 42, 50, 1, 1, 4, 41, 42, 190, 80, 1, 1, 4, 51, 42, 400, 152, 154, 1, 1, 4, 61, 42, 680, 152, 802, 220, 1, 1, 4, 71, 42, 1030, 152, 1792, 590, 375, 1, 1, 4, 81, 42, 1450, 152, 2962, 690, 2091, 444, 1
Offset: 3

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Author

Keywords

Comments

We use "cell" in the sense of planar graph theory, meaning a "region" or two-dimensional face.
We start at generation 0 with a regular n-gon with a single cell.
At each stage the mitosis process splits each cell into smaller cells by drawing chords between every pair of points on the boundary of that cell.
For the first few generations of mitosis of a triangle, square, pentagon, and hexagon, see the sketch in one of the links below.
The process of going from generation 0 to generation 1 was analyzed by Poonen and Rubinstein (1998) - see A007678 and A331450.
It is worth enlarging the illustrations in order to see the detailed structure and the cell counts in the upper left corner. The illustrations for the mitosis of a 7-gon can be seen in A349808 and are not repeated here.
Conjecture 1: For a fixed value of n, there are integers r and s, which are small compared to n, such that T(n,k) is a polynomial in k of degree r for all k >= s.
For example, T(11,k) = 220*k^2 + 1452*k - 1693 for k >= 2. See the Formulas section below for further examples.
Note that if n is odd, all generations of mitosis of a regular n-gon contain a (smaller) regular n-gon at their center.
Conjecture 2: Apart from the central n-gon when n is odd, any cell will eventually split into a mixture of triangles and pentagons.
If we think of triangles and pentagons are harmless cells, and all other cells as dangerous, the conjecture states that (with the exception of the central odd cells), all cells eventually become harmless.

Examples

			The table begins:
.
      |               Number of polygons after k generations
  n\k | 0,    1,     2,     3,      4,      5,      6,      7,      8,      9, ...
----------------------------------------------------------------------------------
   3  | 1,    1,     1,     1,      1,      1,      1,      1,      1,      1, ...
   4  | 1,    4,     4,     4,      4,      4,      4,      4,      4,      4, ...
   5  | 1,   11,    21,    31,     41,     51,     61,     71,     81,     91, ...
   6  | 1,   24,    42,    42,     42,     42,     42,     42,     42,     42, ...
   7  | 1,   50,   190,   400,    680,   1030,   1450,   1940,   2500,   3130, ...
   8  | 1,   80,   152,   152,    152,    152,    152,    152,    152,    152, ...
   9  | 1,  154,   802,  1792,   2962,   4312,   5842,   7552,   9442,  11512, ...
  10  | 1,  220,   590,   690,    790,    890,    990,   1090,   1190,   1290, ...
  11  | 1,  375,  2091,  4643,   7635,  11067,  14939,  19251,  24003,  29195, ...
  12  | 1,  444,   948,   948,    948,    948,    948,    948,    948,    948, ...
  13  | 1,  781,  5461, 14119,  24727,  37285,  51793,  68251,  86659, 107017, ...
  14  | 1,  952,  3066,  4046,   5026,   6006,   6986,   7966,   8946,   9926, ...
  15  | 1, 1456,  9361, 22756,  40186,  61066,  85396, 113176, 144406, 179086, ...
  16  | 1, 1696,  6096,  8240,   9520,  10800,  12080,  13360,  14640,  15920, ...
  17  | 1, 2500, 18225, 49131,  90883, 143175, 206007, 279379, 363291, 457743, ...
  18  | 1, 2466,  7344, 10872,  14166,  16866,  19566,  22266,  24966,  27666, ...
  19  | 1, 4029, 29356, 77616, 140316, 217456, 309036, 415056, 535516, 670416, ...
  20  | 1, 4500, 19580, 31620,  39820,  48020,  56220,  64420,  72620,  80820, ...
  21  | 1, 6175, 40720, 97336, 168022, 252778, 351604, 464500, 591466, 732502, ...
  22  | 1, 6820, 31042, 52030,  65890,  79750,  93610, 107470, 121330, 135190, ...
.
		

Crossrefs

Cf. A007678 (column 1), A349807 (column 2), A017281 (row 5), A349808 (row 7); also A350501, A350502.
Cf. also A331450, A349967, A349968.

Formula

Formulas for the initial rows: (These are easy to prove.)
To avoid double subscripts, we use a(k) for T(n,k) when we are looking at row n.
n=3: a(k) = 1, for k >= 0.
n=4: a(0) = 1, a(k) = 4 for k >= 1.
n=5: a(k) = 10k+1, k >= 0. See A017281.
n=6: a(0) = 1, a(1) = 24, a(k) = 42 for k >= 2.
n=7: a(0) = 1, a(k) = 35*k^2+35*k-20 for k >= 1. See A349808.
n=8: a(0) = 1, a(1) = 80, a(k) = 152 for k >= 2.
n=9: a(0) = 1, a(1) = 154, a(k) = 90*k^2+540*k-638 for k >= 2.
n=10: a(0) = 1, a(1) = 220, a(k) = 100*k+390 for k >= 2.
n=11: a(0) = 1, a(1) = 375, a(k) = 220*k^2 + 1452*k - 1693 for k >= 2.
n=12: a(0) = 1, a(1) = 444, a(k) = 948 for k >= 2.
n=13: a(0) = 1, a(1) = 781, a(k) = 975*k^2 + 3783*k - 6005 for k >= 2.
n=14: a(0) = 1, a(k) = 980*k + 1106 for k >= 1.
n=15: a(k) = 1725*k^2+5355*k-8834 for k >= 3.
n=16: a(k) = 1280*k + 4400 for k >= 3.
n=18: a(k) = 2700*k + 3366 for k >= 4.
Also T(n,1) = A007678(n).

A161709 a(n) = 22*n + 1.

Original entry on oeis.org

1, 23, 45, 67, 89, 111, 133, 155, 177, 199, 221, 243, 265, 287, 309, 331, 353, 375, 397, 419, 441, 463, 485, 507, 529, 551, 573, 595, 617, 639, 661, 683, 705, 727, 749, 771, 793, 815, 837, 859, 881, 903, 925, 947, 969, 991, 1013, 1035, 1057, 1079, 1101, 1123
Offset: 0

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Author

Reinhard Zumkeller, Jun 17 2009

Keywords

References

  • Italo Ghersi, Matematica dilettevole e curiosa, p. 139, Hoepli, Milano, 1967. [From Vincenzo Librandi, Dec 02 2009]

Crossrefs

Programs

Formula

From G. C. Greubel, Sep 18 2019: (Start)
a(n) = 2*a(n-1) - a(n-2).
G.f.: (1 + 21*x)/(1-x)^2.
E.g.f.: (1 + 22*x)*exp(x). (End)

A139222 a(n) = 30*n - 27.

Original entry on oeis.org

3, 33, 63, 93, 123, 153, 183, 213, 243, 273, 303, 333, 363, 393, 423, 453, 483, 513, 543, 573, 603, 633, 663, 693, 723, 753, 783, 813, 843, 873, 903, 933, 963, 993, 1023, 1053, 1083, 1113, 1143, 1173, 1203, 1233, 1263, 1293, 1323, 1353, 1383, 1413, 1443, 1473
Offset: 1

Views

Author

Odimar Fabeny, Jun 06 2008

Keywords

Comments

Multiples of 3 with the units digit equal to 3.

Crossrefs

Subsequence of A034709, together with A017281, A017293, A139245, A017329, A139249, A139264, A139279 and A139280.

Programs

Formula

a(n) = a(n-1) + 30.
From Elmo R. Oliveira, Apr 04 2025: (Start)
G.f.: 3*x*(1+9*x)/(1-x)^2.
E.g.f.: 3*(exp(x)*(10*x - 9) + 9).
a(n) = 3*A017281(n-1) = A139280(n)/3.
a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)

Extensions

More terms from Reinhard Zumkeller, Jun 22 2008

A139249 a(n) = 30*n - 24.

Original entry on oeis.org

6, 36, 66, 96, 126, 156, 186, 216, 246, 276, 306, 336, 366, 396, 426, 456, 486, 516, 546, 576, 606, 636, 666, 696, 726, 756, 786, 816, 846, 876, 906, 936, 966, 996, 1026, 1056, 1086, 1116, 1146, 1176, 1206, 1236, 1266, 1296, 1326, 1356, 1386, 1416, 1446, 1476
Offset: 1

Views

Author

Odimar Fabeny, Jun 06 2008, Jun 07 2008

Keywords

Comments

Multiples of 6 with unit digit equal to 6.

Crossrefs

Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139264, A139279 and A139280. - Reinhard Zumkeller, Jun 22 2008
Cf. A016861.

Programs

Formula

a(n) = a(n-1) + 30.
From Elmo R. Oliveira, Apr 04 2025: (Start)
G.f.: 6*x*(1+4*x)/(1-x)^2.
E.g.f.: 6*(exp(x)*(5*x - 4) + 4).
a(n) = 6*A016861(n-1).
a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)

Extensions

More terms from Reinhard Zumkeller, Jun 22 2008
Edited by R. J. Mathar, Jul 20 2008

A139264 a(n) = 70*n - 63.

Original entry on oeis.org

7, 77, 147, 217, 287, 357, 427, 497, 567, 637, 707, 777, 847, 917, 987, 1057, 1127, 1197, 1267, 1337, 1407, 1477, 1547, 1617, 1687, 1757, 1827, 1897, 1967, 2037, 2107, 2177, 2247, 2317, 2387, 2457, 2527, 2597, 2667, 2737, 2807, 2877, 2947, 3017, 3087, 3157, 3227
Offset: 1

Views

Author

Odimar Fabeny, Jun 06 2008

Keywords

Comments

Multiples of 7 with unit digit equal to 7.

Crossrefs

Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139249, A139279 and A139280.

Programs

Formula

a(n) = a(n-1) + 70.
From Elmo R. Oliveira, Apr 04 2025: (Start)
G.f.: 7*x*(1+9*x)/(1-x)^2.
E.g.f.: 7*(exp(x)*(10*x - 9) + 9).
a(n) = 7*A017281(n-1).
a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)

Extensions

More terms from Reinhard Zumkeller, Jun 22 2008

A161714 a(n) = 28*n + 1.

Original entry on oeis.org

1, 29, 57, 85, 113, 141, 169, 197, 225, 253, 281, 309, 337, 365, 393, 421, 449, 477, 505, 533, 561, 589, 617, 645, 673, 701, 729, 757, 785, 813, 841, 869, 897, 925, 953, 981, 1009, 1037, 1065, 1093, 1121, 1149, 1177, 1205, 1233, 1261, 1289, 1317, 1345, 1373
Offset: 0

Views

Author

Reinhard Zumkeller, Jun 17 2009

Keywords

Crossrefs

Programs

Formula

G.f.: (1 + 27*x)/(1-x)^2. - Indranil Ghosh, Apr 05 2017
E.g.f.: (1 + 28*x)*exp(x). - G. C. Greubel, Sep 18 2019

A062332 Primes starting and ending with 1.

Original entry on oeis.org

11, 101, 131, 151, 181, 191, 1021, 1031, 1051, 1061, 1091, 1151, 1171, 1181, 1201, 1231, 1291, 1301, 1321, 1361, 1381, 1451, 1471, 1481, 1511, 1531, 1571, 1601, 1621, 1721, 1741, 1801, 1811, 1831, 1861, 1871, 1901, 1931, 1951, 10061, 10091, 10111, 10141
Offset: 1

Views

Author

Amarnath Murthy, Jun 21 2001

Keywords

Comments

Complement of A208261 (nonprime numbers with all divisors starting and ending with digit 1) with respect to A208262 (numbers with all divisors starting and ending with digit 1). - Jaroslav Krizek, Mar 04 2012
Intersection of A030430 and A045707. - Michel Marcus, Jun 08 2013

Examples

			102701 is a member as it is a prime and the first and the last digits are both 1.
		

Crossrefs

Cf. A208259 (Numbers starting and ending with digit 1).

Programs

  • Haskell
    a062332 n = a062332_list !! (n-1)
    a062332_list = filter ((== 1) . a010051') a208259_list
    -- Reinhard Zumkeller, Jul 16 2014
  • Mathematica
    fl1Q[n_]:=Module[{idn=IntegerDigits[n]},First[idn]==Last[idn]==1]; Select[ Prime[Range[1300]],fl1Q] (* Harvey P. Dale, Apr 30 2012 *)
  • PARI
    { n=-1; t=log(10); forprime (p=2, 5*10^5, if ((p-10*(p\10)) == 1 && (p\10^(log(p)\t)) == 1, write("b062332.txt", n++, " ", p); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 05 2009
    

Formula

A010051(a(n)) * A000030(a(n)) * (a(n) mod 10) = 1. - Reinhard Zumkeller, Jul 16 2014

Extensions

Corrected and extended by Larry Reeves (larryr(AT)acm.org), Jun 29 2001
Missing term a(36)=1901 added by Harry J. Smith, Aug 05 2009

A086273 Rectangular array T(n,k) of central polygonal numbers, by antidiagonals.

Original entry on oeis.org

1, 1, 3, 1, 4, 7, 1, 5, 10, 13, 1, 6, 13, 19, 21, 1, 7, 16, 25, 31, 31, 1, 8, 19, 31, 41, 46, 43, 1, 9, 22, 37, 51, 61, 64, 57, 1, 10, 25, 43, 61, 76, 85, 85, 73, 1, 11, 28, 49, 71, 91, 106, 113, 109, 91, 1, 12, 31, 55, 81, 106, 127, 141, 145, 136, 111, 1, 13, 34, 61, 91, 121, 148
Offset: 1

Views

Author

Clark Kimberling, Jul 14 2003

Keywords

Comments

Transpose of the array at A086272.

Examples

			Northwest corner:
  1    1    1    1    1    1    1    1    1    1
  3    4    5    6    7    8    9   10   11   12 A000027
  7   10   13   16   19   22   25   28   31   34 A112414, A016777
  13   19   25   31   37   43   49   55   61   67 A016921
  21   31   41   51   61   71   81   91  101  111 A017281
  31   46   61   76   91  106  121  136  151  166
  43   64   85  106  127  148  169  190  211  232
  57   85  113  141  169  197  225  253  281  309
  73  109  145  181  217  253  289  325  361  397
  91  136  181  226  271  316  361  406  451  496
111  166  221  276  331  386  441  496  551  606
133  199  265  331  397  463  529  595  661  727
157  235  313  391  469  547  625  703  781  859
183  274  365  456  547  638  729  820  911 1002
211  316  421  526  631  736  841  946 1051 1156
241  361  481  601  721  841  961 1081 1201 1321
		

Crossrefs

Programs

Formula

T(n, k)=(k+1)*binomial(n, 2)+1.

A144433 Multiples of 8 interleaved with the sequence of odd numbers >= 3.

Original entry on oeis.org

8, 3, 16, 5, 24, 7, 32, 9, 40, 11, 48, 13, 56, 15, 64, 17, 72, 19, 80, 21, 88, 23, 96, 25, 104, 27, 112, 29, 120, 31, 128, 33, 136, 35, 144, 37, 152, 39, 160, 41, 168, 43, 176, 45, 184, 47, 192, 49, 200, 51, 208, 53, 216, 55, 224, 57, 232, 59, 240, 61, 248, 63, 256, 65, 264
Offset: 1

Views

Author

Paul Curtz, Oct 04 2008

Keywords

Comments

For n >= 2, these are the numerators of 1/n^2 - 1/(n+1)^2: A061037(4), A061039(5), A061041(6), A061043(7), A061045(8), A061047(9), A061049(10), etc.

Crossrefs

Cf. A120070.

Programs

Formula

a(2*n+1) = A008590(n+1), a(2*n) = A005408(n).
a(2*n+1) + a(2*n+2) = A017281(n+1).
From R. J. Mathar, Apr 01 2009: (Start)
a(n) = 2*a(n-2) - a(n-4).
G.f.: x*(8+3*x-x^3)/((1-x)^2*(1+x)^2). (End)
a(n) = (n + 1) * 4^(n mod 2). - Wesley Ivan Hurt, Nov 27 2013

Extensions

Edited by R. J. Mathar, Apr 01 2009
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