A139245 -id:A139245 - cp's OEIS frontend

A346651 a(n) is the number of divisors of A139245(n) ending with 2.

1, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 3, 2, 4, 2, 2, 3, 2, 3, 4, 2, 2, 3, 2, 3, 5, 2, 3, 3, 2, 2, 4, 3, 2, 3, 4, 2, 4, 2, 3, 3, 2, 2, 5, 3, 2, 6, 2, 2, 4, 2, 3, 3, 3, 2, 4, 2, 4, 3, 3, 3, 5, 2, 2, 3, 2, 2, 7, 4, 2, 4, 2, 2, 4, 3, 3, 3, 2, 3, 6, 2, 3, 3, 4, 2, 4, 2, 2, 5, 2

Offset: 1

Stefano Spezia, Jul 26 2021

a(n) is odd if and only if A139245(n) either is the square of a number ending with 2 or has a unitary prime divisor ending with 7.

The term 1 appears only for n = 1 in corresponding to A139245(1) = 4.

			a(14) = 4 since there are 4 divisors of A139245(14) = 264 ending with 2: 2, 12, 22 and 132.

Cf. A000005, A017293 (numbers ending with 2), A017294 (squares of numbers ending with 2), A030432, A056169, A139245 (product of two numbers ending with 2), A346388, A346389.

a[n_]:=Length[Drop[Select[Divisors[20n-16], (Last[IntegerDigits[#]]==2&)]]]; Array[a, 90]

a(n) = sumdiv(20*n-16, d, (d%10) == 2); \\ Michel Marcus, Jul 26 2021

A017281 a(n) = 10*n + 1.

Original entry on oeis.org

1, 11, 21, 31, 41, 51, 61, 71, 81, 91, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 201, 211, 221, 231, 241, 251, 261, 271, 281, 291, 301, 311, 321, 331, 341, 351, 361, 371, 381, 391, 401, 411, 421, 431, 441, 451, 461, 471, 481, 491, 501, 511, 521, 531

Offset: 0

N. J. A. Sloane

Equals [1, 2, 3, ...] convolved with [1, 9, 0, 0, 0, ...]. - Gary W. Adamson, May 30 2009
Let A be the Hessenberg matrix of order n, defined by: A[1,j]=1, A[i,i]:=10, (i>1), A[i,i-1] = -1, and A[i,j]=0 otherwise. Then, for n>=2, a(n-1) = -coeff(charpoly(A,x),x^(n-1)). - Milan Janjic, Feb 21 2010
Positive integers with last decimal digit = 1. - Wesley Ivan Hurt, Jun 17 2015
Also the number of (not necessarily maximal) cliques in the 2n-crossed prism graph. - Eric W. Weisstein, Nov 29 2017
From Martin Renner, May 28 2024: (Start)
Also number of squares in a grid cross with equally long arms and a width of two points (cf. A017113), e.g. for n = 2 there are nine squares of size 1 unit of area, four of size 2, two of size 5, four of size 8 and two of size 13, thus a total of 21 squares.
    · ·           · ·           · ·           · ·           * ·
    · ·           · ·           * ·           * ·           · ·
* * · · · ·   · · * · · ·   · · · · * ·   · · · · · ·   · · · · · *
* * · · · ·   · * · * · ·   · * · · · ·   * · · · * ·   * · · · · ·
    · ·           * ·           · *           · ·           · ·
    · ·           · ·           · ·           * ·           · *
The possible areas of the squares are given by ceiling(k^2/2) for 1 <= k <= 2*n+1, cf. A000982. In general, there are 4*n + 1 squares with one unit area to be found in the cross, cf. A016813, for n > 0 always four squares of even area and two squares of odd area > 1. (End)

G. C. Greubel, Table of n, a(n) for n = 0..1000
Milan Janjic, Hessenberg Matrices and Integer Sequences, J. Int. Seq. 13 (2010) # 10.7.8.
Tanya Khovanova, Recursive Sequences
Eric Weisstein's World of Mathematics, Clique
Eric Weisstein's World of Mathematics, Crossed Prism Graph
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Cf. A093645 (column 1).
Subsequence of A034709, together with A017293, A017329, A139222, A139245, A139249, A139264, A139279 and A139280.
Cf. A048161, A154428.
Cf. A005408, A016813, A016921, A017533, A161700, A128470, A158057, A161705, A161709, A161714.
Cf. A030430 (primes).
Cf. A272914, first comment. [Bruno Berselli, May 26 2016]

List([0..60], n-> 10*n+1 ); # G. C. Greubel, Sep 18 2019

a017281 = (+ 1) . (* 10)
a017281_list = [1,11..]  -- Reinhard Zumkeller, Apr 16 2012

[10*n+1 : n in [0..60]]; // Zaki Khandaker, May 16 2015

A017281:=n->10*n + 1; seq(A017281(n), n=0..80); # Wesley Ivan Hurt, Jan 29 2014

f[n_] := FromDigits[IntegerDigits[n^2, n + 1]]; Array[f, 60] (* Robert G. Wilson v, Apr 14 2009 *)
Range[1, 1000, 10] (* Vladimir Joseph Stephan Orlovsky, May 28 2011 *)
(* From Eric W. Weisstein, Nov 29 2017: (Start) *)
Table[10n+1, {n, 0, 60}]
10*Range[0, 60] + 1
LinearRecurrence[{2, -1}, {11, 21}, {0, 60}]
CoefficientList[Series[(1+9x)/(1-x)^2, {x, 0, 60}], x] (* End *)

Vec((1+9*x)/(1-x)^2 + O(x^80)) \\ Michel Marcus, Jun 17 2015

[10*n+1 for n in (0..60)] # G. C. Greubel, Sep 18 2019

G.f.: (1+9*x)/(1-x)^2.
a(n) = 20*n - a(n-1) - 8, with a(0)=1. - Vincenzo Librandi, Nov 20 2010
a(n) = 2*a(n-1) - a(n-2), for n > 2. - Wesley Ivan Hurt, Jun 17 2015
E.g.f.: (1 + 10*x)*exp(x). - G. C. Greubel, Sep 18 2019

A017329 a(n) = 10*n + 5.

Original entry on oeis.org

5, 15, 25, 35, 45, 55, 65, 75, 85, 95, 105, 115, 125, 135, 145, 155, 165, 175, 185, 195, 205, 215, 225, 235, 245, 255, 265, 275, 285, 295, 305, 315, 325, 335, 345, 355, 365, 375, 385, 395, 405, 415, 425, 435, 445, 455, 465, 475, 485, 495, 505, 515, 525, 535

Offset: 0

N. J. A. Sloane

Continued fraction expansion of tanh(1/5). - Benoit Cloitre, Dec 17 2002
n such that 5 divides the numerator of B(2n) where B(2n) = the 2n-th Bernoulli number. - Benoit Cloitre, Jan 01 2004
5 times odd numbers. - Omar E. Pol, May 02 2008
5th transversal numbers (or 5-transversal numbers): Numbers of the 5th column of positive numbers in the square array of nonnegative and polygonal numbers A139600. Also, numbers of the 5th column in the square array A057145. - Omar E. Pol, May 02 2008
Successive sums: 5, 20, 45, 80, 125, ... (see A033429). - Philippe Deléham, Dec 08 2011
3^a(n) + 1 is divisible by 61. - Vincenzo Librandi, Feb 05 2013
If the initial 5 is changed to 1, giving 1,15,25,35,45,..., these are values of m such that A323288(m)/m reaches a new record high value. - N. J. A. Sloane, Jan 23 2019

A. H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 189. - From N. J. A. Sloane, Dec 01 2012

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Tanya Khovanova, Recursive Sequences.
Index to sequences related to polygonal numbers.
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Cf. A000367, A002193, A016957, A057145, A094884, A139600, A139606, A182007.
Subsequence of A034709, together with A017281, A017293, A139222, A139245, A139249, A139264, A139279 and A139280.
Cf. A005408, A008587, A033429, A267541, A323288.

a017329 = (+ 5) . (* 10)
a017329_list = [5, 15 ..]  -- Reinhard Zumkeller, Apr 10 2015

[10*n + 5: n in [0..60]]; // Vincenzo Librandi, Feb 05 2013

Range[5, 1000, 10] (* Vladimir Joseph Stephan Orlovsky, May 28 2011 *)
LinearRecurrence[{2,-1},{5,15},60] (* Harvey P. Dale, Nov 16 2019 *)

a(n)=10*n+5 \\ Charles R Greathouse IV, Sep 24 2015

a(n) = 5*A005408(n). - Omar E. Pol, Oct 19 2008
a(n) = 20*n - a(n-1) (with a(0)=5). - Vincenzo Librandi, Nov 19 2010
G.f.: 5*(x+1)/(x-1)^2. - Colin Barker, Nov 14 2012
a(n) = A057145(n+2,5). - R. J. Mathar, Jul 28 2016
E.g.f.: 5*exp(x)*(1 + 2*x). - Stefano Spezia, Feb 14 2020
Sum_{n>=0} (-1)^n/a(n) = Pi/20. - Amiram Eldar, Dec 12 2021
From Amiram Eldar, Nov 23 2024: (Start)
Product_{n>=0} (1 - (-1)^n/a(n)) = sqrt(5-sqrt(5))/2 = sqrt(2)*sin(Pi/5) = A182007/A002193.
Product_{n>=0} (1 + (-1)^n/a(n)) = phi/sqrt(2) (A094884). (End)
a(n) = (n+3)^2 - (n-2)^2. - Alexander Yutkin, Mar 16 2025
From Elmo R. Oliveira, Apr 12 2025: (Start)
a(n) = 2*a(n-1) - a(n-2).
a(n) = A008587(2*n+1). (End)

A034709 Numbers divisible by their last digit.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 15, 21, 22, 24, 25, 31, 32, 33, 35, 36, 41, 42, 44, 45, 48, 51, 52, 55, 61, 62, 63, 64, 65, 66, 71, 72, 75, 77, 81, 82, 84, 85, 88, 91, 92, 93, 95, 96, 99, 101, 102, 104, 105, 111, 112, 115, 121, 122, 123, 124, 125, 126, 128, 131, 132

Offset: 1

Erich Friedman

Union of A017281, A017293, A139222, A139245, A017329, A139249, A139264, A139279 and A139280. - Reinhard Zumkeller, Jun 22 2008
The differences between consecutive terms repeat with period 1177 and the corresponding terms differ by 2520 = LCM(1,2,...,9). In other words, a(k*1177+i) = 2520*k + a(i). - Giovanni Resta, Aug 20 2015
The asymptotic density of this sequence is 1177/2520 = 0.467063... (see A341431 and A341432 for the values in other base representations). - Amiram Eldar, Nov 24 2022

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A010879, A034838, A007602.
Cf. A017281, A017293, A139222, A139245, A017329, A139249, A139264, A139279, A139280.
Cf. A341431, A341432.

import Data.Char (digitToInt)
a034709 n = a034709_list !! (n-1)
a034709_list =
   filter (\i -> i `mod` 10 > 0 && i `mod` (i `mod` 10) == 0) [1..]
-- Reinhard Zumkeller, Jun 19 2011

N:= 1000: # to get all terms <= N
sort([seq(seq(ilcm(10,d)*x+d, x=0..floor((N-d)/ilcm(10,d))), d=1..9)]); # Robert Israel, Aug 20 2015

dldQ[n_]:=Module[{idn=IntegerDigits[n],last1},last1=Last[idn]; last1!= 0&&Divisible[n,last1]]; Select[Range[150],dldQ]  (* Harvey P. Dale, Apr 25 2011 *)
Select[Range[150],Mod[#,10]!=0&&Divisible[#,Mod[#,10]]&] (* Harvey P. Dale, Aug 07 2022 *)

for(n=1,200,if(n%10,if(!(n%digits(n)[#Str(n)]),print1(n,", ")))) \\ Derek Orr, Sep 19 2014

A034709_list = [n for n in range(1, 1000) if n % 10 and not n % (n % 10)]
# Chai Wah Wu, Sep 18 2014

A017293 a(n) = 10*n + 2.

Original entry on oeis.org

2, 12, 22, 32, 42, 52, 62, 72, 82, 92, 102, 112, 122, 132, 142, 152, 162, 172, 182, 192, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 302, 312, 322, 332, 342, 352, 362, 372, 382, 392, 402, 412, 422, 432, 442, 452, 462, 472, 482, 492, 502, 512, 522, 532

Offset: 0

N. J. A. Sloane, Dec 11 1996

Number of 5 X n 0-1 matrices avoiding simultaneously the right angled numbered polyomino patterns (ranpp) (00;1), (01;0), (11;0) and (01;1). An occurrence of a ranpp (xy;z) in a matrix A=(a(i,j)) is a triple (a(i1,j1), a(i1,j2), a(i2,j1)) where i1A008574; m=3: A016933; m=4: A022144; m=6: A017569. - Sergey Kitaev, Nov 13 2004

Vincenzo Librandi, Table of n, a(n) for n = 0..5000
Tanya Khovanova, Recursive Sequences.
Sergey Kitaev, On multi-avoidance of right angled numbered polyomino patterns, Integers: Electronic Journal of Combinatorial Number Theory 4 (2004), A21, 20pp.
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Subsequence of A034709, together with A017281, A139222, A139245, A017329, A139249, A139264, A139279 and A139280.

Cf. A008574, A008592, A016861, A016873, A016933, A017569, A022144.

[10*n+2: n in [0..50]]; // Vincenzo Librandi, May 04 2011

A017293:=n->10*n+2; seq(A017293(n), n=0..100); # Wesley Ivan Hurt, May 03 2014

Range[2, 1000, 10] (* Vladimir Joseph Stephan Orlovsky, May 28 2011 *)
CoefficientList[Series[(2 + 8 x) / (1 - x)^2, {x, 0, 30}], x] (* Vincenzo Librandi, Jul 23 2016 *)
10 Range[0,60]+2 (* or *) LinearRecurrence[{2,-1},{2,12},60] (* Harvey P. Dale, Jul 04 2019 *)

a(n) = 2*A016861(n) = A008592(n) + 2. - Wesley Ivan Hurt, May 03 2014
G.f.: 2*(1 + 4*x)/(1-x)^2. - Vincenzo Librandi, Jul 23 2016
From Elmo R. Oliveira, Apr 04 2025: (Start)
E.g.f.: 2*exp(x)*(1 + 5*x).
a(n) = 2*a(n-1) - a(n-2) for n >= 2.
a(n) = A016873(2*n). (End)

A139279 a(n) = 40*n - 32.

Original entry on oeis.org

8, 48, 88, 128, 168, 208, 248, 288, 328, 368, 408, 448, 488, 528, 568, 608, 648, 688, 728, 768, 808, 848, 888, 928, 968, 1008, 1048, 1088, 1128, 1168, 1208, 1248, 1288, 1328, 1368, 1408, 1448, 1488, 1528, 1568, 1608, 1648, 1688, 1728, 1768, 1808, 1848

Offset: 1

Odimar Fabeny, Jun 06 2008

Multiples of 8 with unit digit equal to 8.

Vincenzo Librandi, Table of n, a(n) for n = 1..2000
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139249, A139264 and A139280.

[40*n-32: n in [1..50]]; // Vincenzo Librandi, Jun 19 2011

NestList[#+40&,8,50] (* Harvey P. Dale, Oct 02 2013 *)

a(n)=40*n-32 \\ Charles R Greathouse IV, Aug 25 2014

a(n) = a(n-1) + 40.
From G. C. Greubel, Jul 18 2017: (Start)
G.f.: (72*x - 32)/(1-x)^2.
E.g.f.: (40*x - 32)*exp(x). (End)

More terms from Reinhard Zumkeller, Jun 22 2008

New definition from Paolo P. Lava, Sep 06 2010

A139280 a(n) = 90*n - 81.

Original entry on oeis.org

9, 99, 189, 279, 369, 459, 549, 639, 729, 819, 909, 999, 1089, 1179, 1269, 1359, 1449, 1539, 1629, 1719, 1809, 1899, 1989, 2079, 2169, 2259, 2349, 2439, 2529, 2619, 2709, 2799, 2889, 2979, 3069, 3159, 3249, 3339, 3429, 3519, 3609, 3699, 3789, 3879, 3969

Offset: 1

Odimar Fabeny, Jun 06 2008

Multiples of 9 with final digit 9.

Vincenzo Librandi, Table of n, a(n) for n = 1..2000
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139249, A139264 and A139279.

Cf. A017281, A139222.

[90*n-81: n in [1..50]]; // Vincenzo Librandi, Jun 19 2011

Table[90*n-81, {n, 0, 50}] (* G. C. Greubel, Jul 18 2017 *)

for(n=1, 1e2, a=90*n-81; print1(a, ", ")) \\ Felix Fröhlich, Jul 07 2014

a(n) = a(n-1) + 90.
From G. C. Greubel, Jul 18 2017: (Start)
G.f.: 9*(19*x-9)/(x-1)^2.
E.g.f.: 81 + 9*(10*x - 9)*exp(x). (End) [G.f. corrected by Georg Fischer, May 12 2019]; [E.g.f. corrected by Elmo R. Oliveira, Apr 04 2025]
From Elmo R. Oliveira, Apr 04 2025: (Start)
a(n) = 9*A017281(n-1) = 3*A139222(n).
a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)

More terms from Reinhard Zumkeller, Jun 22 2008

A346950 Positive integers k that are the product of two integers ending with 3.

Original entry on oeis.org

9, 39, 69, 99, 129, 159, 169, 189, 219, 249, 279, 299, 309, 339, 369, 399, 429, 459, 489, 519, 529, 549, 559, 579, 609, 639, 669, 689, 699, 729, 759, 789, 819, 849, 879, 909, 939, 949, 969, 989, 999, 1029, 1059, 1079, 1089, 1119, 1149, 1179, 1209, 1219, 1239, 1269

Offset: 1

Stefano Spezia, Aug 08 2021

All the terms end with 9 (A017377).

			9 = 3*3, 39 = 3*13, 69 = 3*23, 99 = 3*33, 129 = 3*43, 159 = 3*53, 169 = 13*13, 189 = 3*63, ...

Stefano Spezia, Table of n, a(n) for n = 1..10000

Cf. A017377 (supersequence), A053742 (ending with 5), A139245 (ending with 2), A324297 (ending with 6), A346951, A346952, A346953.

a={}; For[n=0, n<=250, n++, For[k=0, k<=n, k++, If[Mod[10*n+9, 10*k+3]==0 && Mod[(10*n+9)/(10*k+3), 10]==3&& 10*n+9>Max[a], AppendTo[a, 10*n+9]]]]; a

def aupto(lim): return sorted(set(a*b for a in range(3, lim//3+1, 10) for b in range(a, lim//a+1, 10)))
print(aupto(1270)) # Michael S. Branicky, Aug 08 2021

Limit_{n->oo} a(n)/a(n-1) = 1.

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

Odimar Fabeny, Jun 06 2008

Multiples of 3 with the units digit equal to 3.

Vincenzo Librandi, Table of n, a(n) for n = 1..2000
Index entries for linear recurrences with constant coefficients, signature (2,-1).

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

[30*n - 27: n in [1..60]]; // Vincenzo Librandi, Jun 17 2011

Range[3, 2000, 30] (* Vladimir Joseph Stephan Orlovsky, Jun 15 2011 *)
30*Range[50]-27 (* or *) NestList[30+#&,3,50] (* Harvey P. Dale, Mar 27 2021 *)

a(n)=30*n-27 \\ Charles R Greathouse IV, Aug 25 2014

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)

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

Odimar Fabeny, Jun 06 2008, Jun 07 2008

Multiples of 6 with unit digit equal to 6.

Vincenzo Librandi, Table of n, a(n) for n = 1..2000
William A. Stein, Dimensions of the spaces S_k(Gamma_0(N)).
Index entries for linear recurrences with constant coefficients, signature (2,-1).

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

Cf. A016861.

[30*n - 24: n in [1..60]]; // Vincenzo Librandi, Jun 19 2011

Range[6,7000,30] (* Vladimir Joseph Stephan Orlovsky, Jun 18 2011 *)
NestList[30+#&,6,50] (* or *) LinearRecurrence[{2,-1},{6,36},50] (* Harvey P. Dale, May 27 2018 *)

a(n)=30*n-24 \\ Charles R Greathouse IV, Aug 25 2014

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)

More terms from Reinhard Zumkeller, Jun 22 2008

Edited by R. J. Mathar, Jul 20 2008

cp's OEIS Frontend

A346651 a(n) is the number of divisors of A139245(n) ending with 2.

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A017281 a(n) = 10*n + 1.

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A017329 a(n) = 10*n + 5.

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A034709 Numbers divisible by their last digit.

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A017293 a(n) = 10*n + 2.

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A139279 a(n) = 40*n - 32.

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A139280 a(n) = 90*n - 81.