A001590 -id:A001590 - cp's OEIS frontend

A278043 Number of 1's in tribonacci representation of n (cf. A278038).

0, 1, 1, 2, 1, 2, 2, 1, 2, 2, 3, 2, 3, 1, 2, 2, 3, 2, 3, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, 2, 3, 3, 4, 3, 4, 2, 3, 3, 4, 3, 4, 4, 1, 2, 2, 3, 2, 3, 3, 2, 3, 3, 4, 3, 4, 2, 3, 3, 4, 3, 4, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 3, 4, 4, 5, 4, 5, 1, 2, 2, 3, 2, 3, 3, 2, 3, 3, 4, 3, 4, 2, 3, 3, 4, 3, 4

Offset: 0

N. J. A. Sloane, Nov 18 2016

N. J. A. Sloane, Table of n, a(n) for n = 0..20000

Cf. A001590, A003726, A007895, A278038, A278042, A278044.

t[1] = 1; t[2] = 2; t[3] = 4; t[n_] := t[n] = t[n - 1] + t[n - 2] + t[n - 3]; a[0] = 0; a[n_] := Module[{s = {}, m = n, k}, While[m > 0, k = 1; While[t[k] <= m, k++]; k--; AppendTo[s, k]; m -= t[k]; k = 1]; DigitCount[Total[2^(s - 1)], 2, 1]]; Array[a, 100, 0] (* Amiram Eldar, Mar 04 2022 *)

a(n) = A000120(A003726(n+1)). - John Keith, May 23 2022

A047080 Triangular array T read by rows: T(h,k)=number of paths from (0,0) to (k,h-k) using step-vectors (0,1), (1,0), (1,1) with no right angles between pairs of consecutive steps.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 3, 3, 3, 1, 1, 4, 5, 5, 4, 1, 1, 5, 8, 9, 8, 5, 1, 1, 6, 12, 15, 15, 12, 6, 1, 1, 7, 17, 24, 27, 24, 17, 7, 1, 1, 8, 23, 37, 46, 46, 37, 23, 8, 1, 1, 9, 30, 55, 75, 83, 75, 55, 30, 9, 1, 1, 10, 38, 79, 118, 143, 143, 118, 79, 38, 10, 1

Offset: 0

Clark Kimberling

T(n,k) equals the number of reduced alignments between a string of length n and a string of length k. See Andrade et. al. - Peter Bala, Feb 04 2018

			E.g., row 3 consists of T(3,0)=1; T(3,1)=2; T(3,2)=2; T(3,3)=1.
Triangle begins:
  1;
  1,  1;
  1,  1,  1;
  1,  2,  2,  1;
  1,  3,  3,  3,  1;
  1,  4,  5,  5,  4,  1;
  1,  5,  8,  9,  8,  5,  1;
  1,  6, 12, 15, 15, 12,  6,  1;

Muniru A Asiru, Table of n, a(n) for n = 0..1325
H. Andrade, I. Area, J. J. Nieto, and A. Torres, The number of reduced alignments between two DNA sequences, BMC Bioinformatics (2014) Vol. 15: 94.

Cf. A047081, A047082, A047083, A047084, A047085, A047086, A047087, A047088.

Cf. A001590, A022856, A028310, A078042, A089071, A091337, A171155.

F:=Factorial;
p:= func< n,k | (&+[ (-1)^j*F(n+k-3*j)/(F(j)*F(n-2*j)*F(k-2*j)): j in [0..Min(Floor(n/2), Floor(k/2))]]) >;
q:= func< n,k | n eq 0 or k eq 0 select 0 else (&+[ (-1)^j*F(n+k-3*j-2)/(F(j)*F(n-2*j-1)*F(k-2*j-1)) : j in [0..Min(Floor((n-1)/2), Floor((k-1)/2))]]) >;
A:= func< n,k | p(n,k) - q(n,k) >;
A047080:= func< n,k | n eq 0 select 1 else A(n-k, k) >;
[[A(n,k): k in [1..6]]: n in [1..6]];
[A047080(n,k): k in [0..n], n in [0..12]]; // G. C. Greubel, Oct 30 2022

T := proc(n, k) option remember; if n < 0 or k > n then return 0 fi;
if n < 3 then return 1 fi; if k < iquo(n,2) then return T(n, n-k) fi;
T(n-1, k-1) + T(n-1, k) - T(n-4, k-2)  end:
seq(seq(T(n,k), k=0..n), n=0..11); # Peter Luschny, Feb 11 2018

T[n_, k_] := T[n, k] = Which[n<0 || k>n, 0, n<3, 1, kJean-François Alcover, Jul 30 2018 *)

f=factorial
def p(n,k): return sum( (-1)^j*f(n+k-3*j)/(f(j)*f(n-2*j)*f(k-2*j)) for j in range(1+min((n//2), (k//2))) )
def q(n,k): return sum( (-1)^j*f(n+k-3*j-2)/(f(j)*f(n-2*j-1)*f(k-2*j-1)) for j in range(1+min(((n-1)//2), ((k-1)//2))) )
def A(n,k): return p(n,k) - q(n,k)
def A047080(n,k): return A(n-k, k)
flatten([[A047080(n,k) for k in range(n+1)] for n in range(14)]) # G. C. Greubel, Oct 30 2022

T(h, k) = T(h-1, k-1) + T(h-1, k) - T(h-4, k-2);
Writing T(h, k) = F(h-k, k), generating function for F is (1-xy)/(1-x-y+x^2y^2).
From Peter Bala, Feb 04 2018: (Start)
T(n, k) = (Sum_{i = 0..A} (-1)^i*(n+k-3*i)!/(i!*(n-2*i)!*(k-2*i)!)) - (Sum_{i = 0..B} (-1)^i*(n+k-3*i-2)!/(i!*(n-2*i-1)!*(k-2*i-1)!)), where A = min{floor(n/2), floor(k/2)} and B = min{floor((n-1)/2), floor((k-1)/2)}.
T(2*n, n) = A171155(n). (End)
From G. C. Greubel, Oct 30 2022: (Start) (formulas for triangle T(n,k))
T(n, n-k) = T(n, k).
T(n, n) = A000012(n).
T(n, n-1) = A028310(n-1).
T(n, n-2) = A089071(n-1) = A022856(n+1).
T(2*n, n-1) = A047087(n).
T(2*n+1, n-1) = A047088(n).
Sum_{k=0..n} T(n, k) = (-1)^n*A078042(n) = A001590(n+3).
Sum_{k=0..n} (-1)^k*T(n, k) = A091337(n+1).
Sum_{k=0..floor(n/2)} T(n, k) = A047084(n). (End)

Sequence recomputed to correct terms from 23rd onward, and recurrence and generating function added by Michael L. Catalano-Johnson (mcj(AT)pa.wagner.com), Jan 14 2000

A047081 a(n) = Sum_{k=0..n} T(n, k), array T as in A047080.

Original entry on oeis.org

1, 2, 3, 6, 11, 20, 37, 68, 125, 230, 423, 778, 1431, 2632, 4841, 8904, 16377, 30122, 55403, 101902, 187427, 344732, 634061, 1166220, 2145013, 3945294, 7256527, 13346834, 24548655, 45152016, 83047505, 152748176, 280947697, 516743378, 950439251, 1748130326, 3215312955, 5913882532, 10877325813

Offset: 0

Clark Kimberling

G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,1).

Cf. A047080, A047082, A047083, A047084, A047085, A047086, A047087, A047088.

Cf. A000073, A254006.

[n le 3 select n else Self(n-1) +Self(n-2) +Self(n-3): n in [1..60]]; // G. C. Greubel, Oct 31 2022

LinearRecurrence[{1,1,1}, {1,2,3}, 61] (* G. C. Greubel, Oct 31 2022 *)

@CachedFunction
def a(n): return (n+1) if (n<3) else a(n-1) +a(n-2) +a(n-3) # a = A047081
[a(n) for n in (0..60)] # G. C. Greubel, Oct 31 2022

From G. C. Greubel, Oct 31 2022: (Start)
G.f.: (1 + x)/(1 - x - x^2 - x^3).
a(n) = A000073(n+1) + A000073(n+2). (End)
a(n) = Sum_{r root of x^3-x^2-x-1} r^n/(-3*r^2+5*r+2). - Fabian Pereyra, Nov 23 2024
a(n) = A001590(n+3). - R. J. Mathar, Mar 28 2025

Data corrected by G. C. Greubel, Oct 31 2022

A089068 a(n) = a(n-1)+a(n-2)+a(n-3)+2 with a(0)=0, a(1)=0 and a(2)=1.

Original entry on oeis.org

0, 0, 1, 3, 6, 12, 23, 43, 80, 148, 273, 503, 926, 1704, 3135, 5767, 10608, 19512, 35889, 66011, 121414, 223316, 410743, 755475, 1389536, 2555756, 4700769, 8646063, 15902590, 29249424, 53798079, 98950095, 181997600, 334745776, 615693473

Offset: 0

Roger L. Bagula, Dec 03 2003

The a(n+2) represent the Kn12 and Kn22 sums of the square array of Delannoy numbers A008288. See A180662 for the definition of these knight and other chess sums. - Johannes W. Meijer, Sep 21 2010

Index entries for linear recurrences with constant coefficients, signature (2,0,0,-1).

Cf. A000931, A000073, A077939, A113300, A001057, A006054, A033505.

Cf. A000073 (Kn11 & Kn21), A089068 (Kn12 & Kn22), A180668 (Kn13 & Kn23), A180669 (Kn14 & Kn24), A180670 (Kn15 & Kn25). - Johannes W. Meijer, Sep 21 2010

Join[{a=0,b=0,c=1},Table[d=a+b+c+2;a=b;b=c;c=d,{n,50}]] (* Vladimir Joseph Stephan Orlovsky, Apr 19 2011 *)
RecurrenceTable[{a[0]==a[1]==0,a[2]==1,a[n]==a[n-1]+a[n-2]+a[n-3]+2}, a[n],{n,40}] (* or *) LinearRecurrence[{2,0,0,-1},{0,0,1,3},40] (* Harvey P. Dale, Sep 19 2011 *)

a(n) = A008937(n-2)+A008937(n-1). - Johannes W. Meijer, Sep 21 2010
a(n) = A018921(n-5)+A018921(n-4), n>4. - Johannes W. Meijer, Sep 21 2010
a(n) = A000073(n+2)-1. - R. J. Mathar, Sep 22 2010
From Johannes W. Meijer, Sep 22 2010: (Start)
a(n) = a(n-1)+A001590(n+1).
a(n) = Sum_{m=0..n} A040000(m)*A000073(n-m).
a(n+2) = Sum_{k=0..floor(n/2)} A008288(n-k+1,k+1).
G.f. = x^2*(1+x)/((1-x)*(1-x-x^2-x^3)). (End)
a(n) = 2*a(n-1)-a(n-4), a(0)=0, a(1)=0, a(2)=1, a(3)=3. - Bruno Berselli, Sep 23 2010

Corrected and information added by Johannes W. Meijer, Sep 22 2010, Oct 22 2010

Definition based on arbitrarily set floating-point precision removed by R. J. Mathar, Sep 30 2010

A247027 Indices of primes in the tetranacci sequence A001631.

Original entry on oeis.org

5, 7, 12, 19, 47, 97, 124, 244, 564, 1037, 12007, 13662, 180039

Offset: 1

Robert Price, Sep 09 2014

a(14) > 2*10^5.

Tony D. Noe and Jonathan Vos Post, Primes in Fibonacci n-step and Lucas n-step Sequences, J. of Integer Sequences, Vol. 8 (2005), Article 05.4.4

Cf. A001590, A001631, A100683, A231574, A231575, A232542, A214899, A230607, A020992, A232498, A214727, A081172, A214752, A141523,A214825, A235862.

a={0,0,1,0}; For[n=4, n<=1000, n++, sum=Plus@@a; If[PrimeQ[sum], Print[n]]; a=RotateLeft[a]; a[[4]]=sum]

A241660 Indices of primes in A001630.

Original entry on oeis.org

3, 4, 7, 19, 62, 94, 722, 5197, 5262, 6182, 14007, 21579, 35354, 75592

Offset: 1

Robert Price, Apr 26 2014

nonn

a(15) > 2*10^5.

Tony D. Noe and Jonathan Vos Post, Primes in Fibonacci n-step and Lucas n-step Sequences, J. of Integer Sequences, Vol. 8 (2005), Article 05.4.4

Cf. A001590, A100683, A231574, A231575, A232542, A214899, A230607, A020992, A232498, A214727, A081172, A214752, A141523,A214825, A235862.

a={0,0,1,2}; Print[3]; For[n=4, n<=1000, n++, sum=Plus@@a; If[PrimeQ[sum], Print[n]]; a=RotateLeft[a]; a[[4]]=sum]

Prepended a(1)=3 and Mathematica program corrected by Robert Price, Sep 09 2014

A059832 A ternary tribonacci triangle: form the triangle as follows: start with 3 single values: 1, 2, 3. Each succeeding row is a concatenation of the previous 3 rows.

Original entry on oeis.org

1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3

Offset: 0

Jason Earls, Feb 25 2001

Alternatively, define a morphism f: 1 -> 2, 2 -> 3, 3 -> 1,2,3; let S(0)=1, S(k) = f(S(k-1)) for k>0; then sequence is the concatenation S(0) S(1) S(2) S(3) ...

			Rows 0, 1, 2, ..., 8, ... of the triangle are:
0, [1]
1, [2]
2, [3]
3, [1, 2, 3]
4, [2, 3, 1, 2, 3]
5, [3, 1, 2, 3, 2, 3, 1, 2, 3]
6, [1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3]
7, [2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3]
8, [3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 1, 2, 3, 3, 1, 2, 3, 2, 3, 1, 2, 3]
...

C. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 273.

N. J. A. Sloane, Table of n, a(n) for n = 0..30121 (Roes 0 through 17, flattened.)
C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review

Cf. A059835. Row sums A001590, row lengths A000213.

Rows 0,3,6,9,12,... converge to A305389, rows 1,4,7,10,... converge to A305390, and rows 2,5,8,11,... converge to A305391.

# To get successive rows of A059832
S:=Array(0..100);
S[0]:=[1];
S[1]:=[2];
S[2]:=[3];
for n from 3 to 12 do
S[n]:=[op(S[n-3]),op(S[n-2]), op(S[n-1])];
lprint(S[n]);
od: # N. J. A. Sloane, Jul 04 2018

a(n) = A059825(n) + 1. - Sean A. Irvine, Oct 11 2022

More terms from Larry Reeves (larryr(AT)acm.org), Feb 26 2001

Entry revised by N. J. A. Sloane, Jun 21 2018

A062544 a(n) = n plus sum of previous three terms.

Original entry on oeis.org

0, 1, 3, 7, 15, 30, 58, 110, 206, 383, 709, 1309, 2413, 4444, 8180, 15052, 27692, 50941, 93703, 172355, 317019, 583098, 1072494, 1972634, 3628250, 6673403, 12274313, 22575993, 41523737, 76374072, 140473832, 258371672, 475219608, 874065145, 1607656459, 2956941247

Offset: 0

Henry Bottomley, Jun 26 2001

It appears that this is the number of nonempty subsets of {1,2,...,n} with no gap of length greater than 3 (a set S has a gap of length d if a and b are in S but no x with aA119407 for the corresponding problem for gaps of length 4. - John W. Layman, Nov 02 2011

a(n-3) is the number of compositions of n with no part divisible by 3 and an odd number of parts congruent to 4 or 5 modulo 6. See Moser & Whitney reference. a(2) = 3 counts (5), (4,1), and (1,4) among the compositions of 5. - Brian Hopkins, Sep 06 2019

			a(5) = 5 + 15 + 7 + 3 = 30.
x + 3*x^2 + 7*x^3 + 15*x^4 + 30*x^5 + 58*x^6 + 110*x^7 + 206*x^8 + 383*x^9 + ...

Harry J. Smith, Table of n, a(n) for n = 0..300
Zuwen Luo and Kexiang Xu, The number of connected sets in Apollonian networks, Applied Mathematics and Computation, Volume 479, 2024. On ResearchGate. See p. 12.
L. Moser and E. L. Whitney, Weighted compositions, Canad. Math. Bull. 4 (1961), 39-43.
Index entries for linear recurrences with constant coefficients, signature (3,-2,0,-1,1).

n plus sum of all previous terms gives A000225, n plus sum of two previous terms gives A001924, n plus previous term gives A000217, n gives A001477.
Cf. A007800, A119407.
Cf. A001590 and A325473.

Join[{c=0},a=b=0;Table[z=b+a+c+n;a=b;b=c;c=z,{n,1,40}]] (* Vladimir Joseph Stephan Orlovsky, Apr 02 2011 *)

{ a=a1=a2=a3=0; for (n=0, 300, write("b062544.txt", n, " ", a+=n + a2 + a3); a3=a2; a2=a1; a1=a ) } \\ Harry J. Smith, Aug 08 2009

{a(n) = if( n<0, n = -n; polcoeff( x^4 / ((1 - x) * (1 - 2*x^3 + x^4)) + x * O(x^n), n), polcoeff( x / ((1 - x) * (1 - 2*x + x^4)) + x * O(x^n), n))} /* Michael Somos, Dec 28 2012 */

a(n) = 3*a(n-1) - 2*a(n-2) - 1*a(n-4) + 1*a(n-5). - Joerg Arndt, Apr 02 2011
a(n) = n + a(n-1) + a(n-2) + a(n-3) =(A001590(n+4) - n - 3)/2.
G.f.: x / ((1 - x) * (1 - 2*x + x^4)). a(n) = 2*a(n-1) - a(n-4) + 1. - Michael Somos, Dec 28 2012
a(n) = A325473(n+3) - (n+3). - Brian Hopkins, Sep 06 2019

A243622 Indices of primes in A214829.

Original entry on oeis.org

1, 2, 4, 10, 11, 12, 13, 58, 63, 89, 132, 157, 426, 457, 506, 613, 1839, 1936, 2042, 2355, 3178, 3782, 8556, 8688, 22152, 23232, 44074, 71770, 222666

Offset: 1

Robert Price, Jun 07 2014

a(30) > 222666.

Tony D. Noe and Jonathan Vos Post, Primes in Fibonacci n-step and Lucas n-step Sequences, J. of Integer Sequences, Vol. 8 (2005), Article 05.4.4

Cf. A001590, A100683, A231574, A231575, A232542, A214899, A230607, A020992, A232498, A214727, A081172, A214752, A141523,A214825, A235862, A214827, A214828.

a={1,7,7}; Print["1"]; Print["2"]; For[n=3, n<=1000, n++, sum=Plus@@a; If[PrimeQ[sum], Print[n]]; a=RotateLeft[a]; a[[3]]=sum]

a(27) corrected by Robert Price, May 22 2019

a(29) from Robert Price, May 23 2019

A294627 Expansion of x(1 + x)/((1-2x)*(1+x+x^2)).

Original entry on oeis.org

0, 1, 2, 3, 7, 14, 27, 55, 110, 219, 439, 878, 1755, 3511, 7022, 14043, 28087, 56174, 112347, 224695, 449390, 898779, 1797559, 3595118, 7190235, 14380471, 28760942, 57521883, 115043767, 230087534, 460175067, 920350135, 1840700270, 3681400539, 7362801079, 14725602158, 29451204315

Offset: 0

Wojciech Florek, Feb 12 2018

A generalized tribonacci (A001590) sequence.
For n > 2, 6*a(n) is the number of quaternary sequences of length n in which all triples (q(i),q(i+1),q(i+2)) contain two (arbitrarily chosen) digits, e.g., 0 and 3.
Similarly, recurrences a(n) = a(n-1) + a(n-2) + k*a(n-3) are related to binary (k=0, the Fibonacci sequence A000045), ternary (k=1, the tribonacci sequence A001590), quinary (k=3) and so on sequences with all triples (t(i),t(i+1),t(i+2)) containing two (arbitrarily chosen) digits (usually 0 and k+1).
For n > 0, a(n) is the number of ways to tile a strip of length n with squares, dominoes, and two colors of trominoes, with the restriction that the first tile cannot be a tromino. - Greg Dresden and Bora Bursalı, Aug 31 2023
For n > 1, a(n) is the number of ways to tile a strip of length n-2 with squares, dominoes, and two colors of trominoes, where the strip begins with an upper level of two cells. For example, when n=7 we have this strip of length 5:
 _
|||_____
|||_|||. - Guanji Chen and Greg Dresden, Jun 17 2024

			For n=4 there are 6*7=42 quaternary sequences of length 4 such that each triple (i.e., exactly two of them: q1,q2,q3 and q2,q3,q4) contain both 0 and 3. They are 003x, 030x, 03y0, 0330, 330x, 303x, 30y3, 3003, 0y30, 3y03, y03x, y30x, where x=0,1,2,3 and y=1,2.

Wojciech Florek, Table of n, a(n) for n = 0..500
Wojciech Florek, A class of generalized Tribonacci sequences applied to counting problems, Appl. Math. Comput., 338 (2018), 809-821.
Index entries for linear recurrences with constant coefficients, signature (1,1,2).

Cf. A000045, A001590, A007040, A033129 (partial sums), A078043, A167373.

LinearRecurrence[{1, 1, 2}, {0, 1, 2}, 50] (* Paolo Xausa, Aug 28 2024 *)

my(x='x+O('x^99)); concat(0, Vec(x*(1+x)/(1-x-x^2-2*x^3))) \\ Altug Alkan, Mar 03 2018

a(n) = a(n-1) + a(n-2) + 2*a(n-3) for n > 2.
a(n+1)/a(n) tends to 2, the unique real root of x^3 - x^2 - x - 2 = 0.
a(n+1) = abs(A078043(n)).
7*a(n) = 3*2^n - A167373(n+1). - R. J. Mathar, Mar 24 2018
E.g.f.: exp(-x/2)*(9*exp(5*x/2) - 9*cos(sqrt(3)*x/2) - sqrt(3)*sin(sqrt(3)*x/2))/21. - Stefano Spezia, Aug 29 2024

cp's OEIS Frontend

A278043 Number of 1's in tribonacci representation of n (cf. A278038).

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A047080 Triangular array T read by rows: T(h,k)=number of paths from (0,0) to (k,h-k) using step-vectors (0,1), (1,0), (1,1) with no right angles between pairs of consecutive steps.

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A047081 a(n) = Sum_{k=0..n} T(n, k), array T as in A047080.

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A089068 a(n) = a(n-1)+a(n-2)+a(n-3)+2 with a(0)=0, a(1)=0 and a(2)=1.

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A247027 Indices of primes in the tetranacci sequence A001631.

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A241660 Indices of primes in A001630.

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A059832 A ternary tribonacci triangle: form the triangle as follows: start with 3 single values: 1, 2, 3. Each succeeding row is a concatenation of the previous 3 rows.

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A294627 Expansion of x(1 + x)/((1-2x)*(1+x+x^2)).