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 21-30 of 721 results. Next

A141060 Fourth quadrisection of Jacobsthal numbers A001045: a(n)=16a(n-1)-5.

Original entry on oeis.org

3, 43, 683, 10923, 174763, 2796203, 44739243, 715827883, 11453246123, 183251937963, 2932031007403, 46912496118443, 750599937895083, 12009599006321323, 192153584101141163, 3074457345618258603, 49191317529892137643
Offset: 0

Views

Author

Paul Curtz, Jul 30 2008

Keywords

Comments

Jacobsthal numbers ending with the decimal digit 3. - Jianing Song, Aug 30 2022

Crossrefs

The other quadrisections of A001045 are A195156 (first), A139792 (second), and A144864 (third).

Programs

Formula

a(n) = A139792(n) + A013776(n).
a(n+1) - a(n) = 10*A013709(n) = 40*A001025(n).
G.f.: (3-8*x)/((1-x)*(1-16*x)). [Colin Barker, Apr 05 2012]
a(0)=3, a(1)=43, a(n)=17*a(n-1)-16*a(n-2). - Harvey P. Dale, Mar 16 2015
From Jianing Song, Aug 30 2022: (Start)
a(n) = A001045(4*n+3).
a(n) = 10*A141032(n) + 3 = 20*A098704(n+1) + 1 = 40*A131865(n-1) + 1 for n >= 1. (End)

A175286 Pisano period of the Jacobsthal sequence A001045 modulo n.

Original entry on oeis.org

1, 1, 6, 2, 4, 6, 6, 2, 18, 4, 10, 6, 12, 6, 12, 2, 8, 18, 18, 4, 6, 10, 22, 6, 20, 12, 54, 6, 28, 12, 10, 2, 30, 8, 12, 18, 36, 18, 12, 4, 20, 6, 14, 10, 36, 22, 46, 6, 42, 20, 24, 12, 52, 54, 20, 6, 18, 28, 58, 12, 60, 10, 18, 2, 12, 30, 66, 8, 66, 12, 70, 18, 18, 36, 60, 18, 30, 12, 78, 4
Offset: 1

Views

Author

R. J. Mathar, Mar 21 2010

Keywords

Examples

			Reading the sequence 0, 1, 1, 3, 5, 11, 21, ... modulo n=3, we get 0, 1, 1, 0, 2, 2, 0, 1, 1, 0, 2, 2, 0, 1, 1, 0, 2, 2, 0, 1, ... = A088689, which has a period (1, 1, 0, 2, 2, 0) of length a(n=3) = 6.
		

Crossrefs

A211893 G.f.: exp( Sum_{n>=1} 3 * Jacobsthal(n)^n * x^n/n ), where Jacobsthal(n) = A001045(n).

Original entry on oeis.org

1, 3, 6, 36, 561, 98211, 43176384, 116622937722, 1022189210900601, 41675008108242048327, 6377839090284322052067558, 4114890941608928235401688095580, 10460015732506081308723488849683574907, 108482611110966450613465001912856742180485969
Offset: 0

Views

Author

Paul D. Hanna, Apr 24 2012

Keywords

Comments

Given g.f. A(x), note that A(x)^(1/3) is not an integer series.

Examples

			G.f.: A(x) = 1 + 3*x + 6*x^2 + 36*x^3 + 561*x^4 + 98211*x^5 + 43176384*x^6 +...
such that
log(A(x))/3 = x + x^2/2 + 3^3*x^3/3 + 5^4*x^4/4 + 11^5*x^5/5 + 21^6*x^6/6 + 43^7*x^7/7 +...+ Jacobsthal(n)^n*x^n/n +...
Jacobsthal numbers begin:
A001045 = [1,1,3,5,11,21,43,85,171,341,683,1365,2731,5461,10923,...].
		

Crossrefs

Cf. A231292 (Jacobsthal(n)^n).

Programs

  • PARI
    {Jacobsthal(n)=polcoeff(x/(1-x-2*x^2+x*O(x^n)),n)}
    {a(n)=polcoeff(exp(sum(k=1, n, 3*Jacobsthal(k)^k*x^k/k)+x*O(x^n)), n)}
    for(n=0, 16, print1(a(n), ", "))

Formula

G.f.: exp( Sum_{n>=1} (2^n - (-1)^n)^n / 3^(n-1) * x^n/n ).

A211895 G.f.: exp( Sum_{n>=1} 3 * Jacobsthal(n)^3 * x^n/n ), where Jacobsthal(n) = A001045(n).

Original entry on oeis.org

1, 3, 6, 36, 186, 1254, 8208, 57540, 404619, 2913705, 21146694, 155231256, 1147302756, 8538393900, 63879354096, 480212156664, 3624581868297, 27456690186507, 208644709097070, 1589982296208492, 12147079485362406, 93012131704072698, 713676733469348352
Offset: 0

Views

Author

Paul D. Hanna, Apr 25 2012

Keywords

Comments

Given g.f. A(x), note that A(x)^(1/3) is not an integer series.

Examples

			G.f.: A(x) = 1 + 3*x + 6*x^2 + 36*x^3 + 186*x^4 + 1254*x^5 + 8208*x^6 +...
such that
log(A(x))/3 = x + x^2/2 + 3^3*x^3/3 + 5^3*x^4/4 + 11^3*x^5/5 + 21^3*x^6/6 + 43^3*x^7/7 +...+ Jacobsthal(n)^3*x^n/n +...
Jacobsthal numbers begin:
A001045 = [1,1,3,5,11,21,43,85,171,341,683,1365,2731,5461,10923,...].
		

Crossrefs

Cf. A211893, A211894, A211896, A207970, A001045 (Jacobsthal).

Programs

  • Mathematica
    CoefficientList[Series[((1+x)*(1+4*x)^3/((1-2*x)^3*(1-8*x)))^(1/9), {x, 0, 20}], x] (* Vaclav Kotesovec, Oct 24 2012 *)
  • PARI
    {Jacobsthal(n)=polcoeff(x/(1-x-2*x^2+x*O(x^n)),n)}
    {a(n)=polcoeff(exp(sum(k=1, n, 3*Jacobsthal(k)^3*x^k/k)+x*O(x^n)), n)}
    for(n=0, 30, print1(a(n), ", "))
    
  • PARI
    {a(n)=polcoeff(( (1+x)*(1+4*x)^3 / ((1-2*x)^3*(1-8*x)+x*O(x^n)) )^(1/9),n)}

Formula

G.f.: ( (1+x)*(1+4*x)^3 / ((1-2*x)^3*(1-8*x)) )^(1/9).
G.f.: exp( Sum_{n>=1} (2^n - (-1)^n)^3 / 9 * x^n/n ).
Recurrence: n*a(n) = (5*n-2)*a(n-1) + 6*(5*n-12)*a(n-2) - 8*(5*n-12)*a(n-3) - 64*(n-4)*a(n-4). - Vaclav Kotesovec, Oct 24 2012
a(n) ~ 3^(2/9)*8^n/(Gamma(1/9)*n^(8/9)). - Vaclav Kotesovec, Oct 24 2012

A293434 a(n) is the sum of the proper divisors of n that are Jacobsthal numbers (A001045).

Original entry on oeis.org

0, 1, 1, 1, 1, 4, 1, 1, 4, 6, 1, 4, 1, 1, 9, 1, 1, 4, 1, 6, 4, 12, 1, 4, 6, 1, 4, 1, 1, 9, 1, 1, 15, 1, 6, 4, 1, 1, 4, 6, 1, 25, 1, 12, 9, 1, 1, 4, 1, 6, 4, 1, 1, 4, 17, 1, 4, 1, 1, 9, 1, 1, 25, 1, 6, 15, 1, 1, 4, 6, 1, 4, 1, 1, 9, 1, 12, 4, 1, 6, 4, 1, 1, 25, 6, 44, 4, 12, 1, 9, 1, 1, 4, 1, 6, 4, 1, 1, 15, 6, 1, 4, 1, 1, 30
Offset: 1

Views

Author

Antti Karttunen, Oct 09 2017

Keywords

Examples

			For n = 15, whose proper divisors are [1, 3, 5], all of them are in A001045, thus a(15) = 1 + 3 + 5 = 9.
For n = 21, whose proper divisors are [1, 3, 7], both 1 and 3 are in A001045, thus a(21) = 1 + 3 = 4.
For n = 21845, whose proper divisors are [1, 5, 17, 85, 257, 1285, 4369], only 1, 5, 85 are in A001045, thus a(21845) = 1 + 5 + 85 = 91.
		

Crossrefs

Programs

  • Mathematica
    With[{s = LinearRecurrence[{1, 2}, {0, 1}, 24]}, Table[DivisorSum[n, # &, And[MemberQ[s, #], # != n] &], {n, 105}]] (* Michael De Vlieger, Oct 09 2017 *)
  • PARI
    A147612aux(n,i) = if(!(n%2),n,A147612aux((n+i)/2,-i));
    A147612(n) = 0^(A147612aux(n,1)*A147612aux(n,-1));
    A293434(n) = sumdiv(n,d,(dA147612(d)*d);
    
  • Python
    from sympy import divisors
    def A293434(n): return sum(d for d in divisors(n,generator=True) if d(m-3).bit_length()) # Chai Wah Wu, Apr 18 2025

Formula

a(n) = Sum_{d|n, dA147612(d)*d.
a(n) = A293432(n) - (A147612(n)*n).

A066488 Composite numbers k which divide A001045(k-1).

Original entry on oeis.org

341, 1105, 1387, 1729, 2047, 2465, 2701, 2821, 3277, 4033, 4369, 4681, 5461, 6601, 7957, 8321, 8911, 10261, 10585, 11305, 13741, 13747, 13981, 14491, 15709, 15841, 16705, 18721, 19951, 23377, 29341, 30121, 30889, 31417, 31609, 31621, 34945
Offset: 1

Views

Author

Robert G. Wilson v, Jan 03 2002

Keywords

Comments

Also composite numbers k such that (2^k - 2)/3 + 1 == 2^k - 1 == 1 (mod k).
An equivalent definition of this sequence: pseudoprimes to base 2 that are not divisible by 3. - Arkadiusz Wesolowski, Nov 15 2011
Conjecture: these are composites k such that 2^M(k-1) == -1 (mod M(k)^2 + M(k) + 1), where M(k) = 2^k - 1. - Amiram Eldar and Thomas Ordowski, Dec 19 2019
These are composites k such that 2^(m-1) == 1 (mod (m+1)^6 - 1), where m = 2^k - 1. - Thomas Ordowski, Sep 17 2023

Crossrefs

Programs

  • Magma
    [k:k in [4..40000]|not IsPrime(k) and ((2^(k-1) + (-1)^k) div 3) mod k eq 0]; // Marius A. Burtea, Dec 20 2019
  • Mathematica
    a[0] = 0; a[1] = 1; a[n_] := a[n] = a[n - 1] + 2a[n - 2]; Select[ Range[50000], IntegerQ[a[ # - 1]/ # ] && !PrimeQ[ # ] && # != 1 & ]
    fQ[n_] := ! PrimeQ@ n && Mod[((2^n - 2)/3 + 1), n] == Mod[2^n - 1, n] == 1; Select[ Range@ 35000, fQ]
  • PARI
    is(n)=n%3 && Mod(2,n)^(n-1)==1 && !isprime(n) && n>1 \\ Charles R Greathouse IV, Sep 18 2013
    

A123641 Triangular array related to sequence A123640 with row sum A001045.

Original entry on oeis.org

1, 0, 1, 1, 0, 2, 0, 1, 0, 4, 1, 0, 2, 0, 8, 0, 1, 0, 4, 0, 16, 1, 0, 2, 0, 8, 0, 32, 0, 1, 0, 4, 0, 16, 0, 64, 1, 0, 2, 0, 8, 0, 32, 0, 128, 0, 1, 0, 4, 0, 16, 0, 64, 0, 256, 1, 0, 2, 0, 8, 0, 32, 0, 128, 0, 512, 0, 1, 0, 4, 0, 16, 0, 64, 0, 256, 0, 1024, 1
Offset: 1

Views

Author

Alford Arnold, Oct 04 2006

Keywords

Examples

			For n>0 A123640 begins
1
0 1
1 0 1 1
0 1 0 0 1 1 1 1
suppressing multiple zeros and counting contiguous ones yields
1
0 1
1 0 2
0 1 0 4
1 0 2 0 8
0 1 0 4 0 16
...
		

Crossrefs

Programs

  • PARI
    a001045(n)=(2^n-(-1)^n)/3;
    lista(nn) = {last = v[2]; nb = 1; s = 0; j = 1; for (i=3, nn, if ((v[i] == last) && (s+v[i] < a001045(j)), nb++; s += v[i];, if (last, w = nb, w = 0); print1(w, ", "); nb = 1; last = v[i]; if (s + v[i] >= a001045(j), s = 0; j++;, s += v[i];);););} \\ Michel Marcus, Feb 09 2014

Extensions

More terms from Michel Marcus, Feb 09 2014

A129738 List of primitive prime divisors of the Jacobsthal numbers A001045 in their order of occurrence.

Original entry on oeis.org

3, 5, 11, 7, 43, 17, 19, 31, 683, 13, 2731, 127, 331, 257, 43691, 73, 174763, 41, 5419, 23, 89, 2796203, 241, 251, 4051, 8191, 87211, 29, 113, 59, 3033169, 151, 715827883, 65537, 67, 20857, 131071, 281, 86171, 37, 109, 1777, 25781083, 524287, 22366891, 61681, 83
Offset: 1

Views

Author

N. J. A. Sloane, May 13 2007

Keywords

Comments

Read A001045 term-by-term, factorize each term, write down any primes not seen before.

Crossrefs

Programs

  • Maple
    concat := (a,h)->[op(a),op(sort(convert(h,list)))]:
    PPDinOrder := proc(S) local A,H,T,s;
    T := {0,1}; A := [];
    for s in S do
      H := numtheory[factorset](s) minus T:
      if H <> {} then
        A := concat(A,H);
        T := T union H
      fi
    od;
    A end:
    A129738 := PPDinOrder(A001045);
    # Peter Luschny, Jan 04 2011
  • Mathematica
    DeleteDuplicates[Flatten[FactorInteger[#][[All,1]]&/@LinearRecurrence[ {1,2},{3,5},50]]](* Harvey P. Dale, Apr 14 2020 *)

A140944 Triangle T(n,k) read by rows, the k-th term of the n-th differences of the Jacobsthal sequence A001045.

Original entry on oeis.org

0, 1, 0, -1, 2, 0, 3, -2, 4, 0, -5, 6, -4, 8, 0, 11, -10, 12, -8, 16, 0, -21, 22, -20, 24, -16, 32, 0, 43, -42, 44, -40, 48, -32, 64, 0, -85, 86, -84, 88, -80, 96, -64, 128, 0, 171, -170, 172, -168, 176, -160, 192, -128, 256, 0, -341, 342, -340, 344, -336, 352, -320, 384, -256, 512, 0
Offset: 0

Views

Author

Paul Curtz, Jul 24 2008

Keywords

Comments

A variant of the triangle A140503, now including the diagonal.
Since the diagonal contains zeros, rows sums are those of A140503.

Examples

			Triangle begins as:
    0;
    1,   0;
   -1,   2,   0;
    3,  -2,   4,  0;
   -5,   6,  -4,  8,   0;
   11, -10,  12, -8,  16,  0;
  -21,  22, -20, 24, -16, 32,  0;
		

Crossrefs

Programs

  • Magma
    [2^k*(1-(-2)^(n-k))/3: k in [0..n], n in [0..15]]; // G. C. Greubel, Feb 18 2023
    
  • Maple
    A001045:= n -> (2^n-(-1)^n)/3;
    A140944:= proc(n,k) if n = 0 then A001045(k); else procname(n-1,k+1)-procname(n-1,k) ; fi; end:
    seq(seq(A140944(n,k),k=0..n),n=0..10); # R. J. Mathar, Sep 07 2009
  • Mathematica
    T[0, 0]=0; T[1, 0]= T[0, 1]= 1; T[0, k_]:= T[0, k]= T[0, k-1] + 2*T[0, k-2]; T[n_, n_]=0; T[n_, k_]:= T[n, k] = T[n-1, k+1] - T[n-1, k]; Table[T[n, k], {n, 0, 10}, {k, 0, n}]//Flatten (* Jean-François Alcover, Dec 17 2014 *)
    Table[2^k*(1-(-2)^(n-k))/3, {n,0,15}, {k,0,n}]//Flatten (* G. C. Greubel, Feb 18 2023 *)
  • PARI
    T(n, k) = (2^k - 2^n*(-1)^(n+k))/3 \\ Jianing Song, Aug 11 2022
    
  • SageMath
    def A140944(n,k): return 2^k*(1 - (-2)^(n-k))/3
    flatten([[A140944(n,k) for k in range(n+1)] for n in range(16)]) # G. C. Greubel, Feb 18 2023

Formula

T(n, k) = T(n-1, k+1) - T(n-1, k). T(0, k) = A001045(k).
T(n, k) = (2^k - 2^n*(-1)^(n+k))/3, for n >= k >= 0. - Jianing Song, Aug 11 2022
From G. C. Greubel, Feb 18 2023: (Start)
T(n, n-1) = A000079(n).
T(2*n, n) = (-1)^(n+1)*A192382(n+1).
T(2*n, n-1) = (-1)^n*A246036(n-1).
T(2*n, n+1) = A083086(n).
T(3*n, n) = -A115489(n).
Sum_{k=0..n} T(n, k) = A052992(n)*[n>0] + 0*[n=0].
Sum_{k=0..n} (-1)^k*T(n, k) = A045883(n).
Sum_{k=0..n} 2^k*T(n, k) = A084175(n).
Sum_{k=0..n} (-2)^k*T(n, k) = (-1)^(n+1)*A109765(n).
Sum_{k=0..n} 3^k*T(n, k) = A091056(n+1).
Sum_{k=0..floor(n/2)} T(n-k, k) = (-1)^(n+1)*A097038(n).
Sum_{k=0..floor(n/2)} (-1)^k*T(n-k, k) = (-1)^(n+1)*A138495(n). (End)

Extensions

Edited and extended by R. J. Mathar, Sep 07 2009

A200375 Product of Catalan and Jacobsthal numbers: a(n) = A000108(n)*A001045(n+1).

Original entry on oeis.org

1, 1, 6, 25, 154, 882, 5676, 36465, 244530, 1657942, 11471668, 80242890, 568080772, 4056976900, 29212908120, 211783889025, 1544811959970, 11328491394990, 83473572128100, 617702666484750, 4588654943721420, 34206312386929020, 255803818897858920, 1918528298674328250, 14427334095935095764
Offset: 0

Views

Author

Paul D. Hanna, Nov 16 2011

Keywords

Comments

More generally, given {S} such that: S(n) = b*S(n-1) + c*S(n-2), |b|>0, |c|>0, then Sum_{n>=0} S(n)*Catalan(n)*x^n = sqrt( (1-2*b*x - sqrt(1-4*b*x-16*c*x^2))/(2*b^2+8*c) )/x.

Examples

			G.f.: A(x) = 1 + x + 2*3*x^2 + 5*5*x^3 + 14*11*x^4 + 42*21*x^5 + 132*43*x^6 + 429*85*x^7 + 1430*171*x^8 +...+ A000108(n)*A001045(n)*x^n +...
The g.f. of the Jacobsthal sequence A001045, F(x) = 1/(1-x-2*x^2), begins:
F(x) = 1 + x + 3*x^2 + 5*x^3 + 11*x^4 + 21*x^5 + 43*x^6 + 85*x^7 + 171*x^8 +...
The g.f. of A200376, where G(x) =  A(x/G(x)), begins:
G(x) = 1 + x + 5*x^2 + 9*x^3 + 37*x^4 + 81*x^5 + 301*x^6 + 729*x^7 +...
in which the odd-indexed coefficients are powers of 9.
		

Crossrefs

Programs

  • Mathematica
    Array[CatalanNumber[# - 1] (2^# - (-1)^#)/3 &, 25] (* Michael De Vlieger, Apr 24 2018 *)
  • PARI
    {a(n) = binomial(2*n, n)/(n+1) * (2^(n+1) + (-1)^n)/3}
    
  • PARI
    {a(n) = polcoef(sqrt((1-2*x - sqrt(1-4*x-32*x^2 +O(x^(n+3))))/2)/(3*x), n)}
    
  • PARI
    {a(n) = polcoef((1/x)*serreverse(x-x^2 - 4*x^3*sum(m=0,n\2,binomial(2*m,m)/(m+1)*3^m*x^(2*m)) +x^3*O(x^n)), n)}

Formula

G.f.: sqrt( (1-2*x - sqrt(1-4*x-32*x^2))/2 )/(3*x).
G.f.: (1/x)*Series_Reversion(x-x^2 - 4*x^3*Sum_{n>=0} A000108(n)*3^n*x^(2*n) ).
G.f. satisfies: A(x) = G(x*A(x)) and G(x) = A(x/G(x)) where G(x) is the g.f. of A200376: G(x) = 1/sqrt(1-10*x^2 + x^4/(1-8*x^2)) + x/(1-9*x^2).
n*(n+1)*a(n) -2*n*(2*n-1)*a(n-1) -8*(2*n-1)*(2*n-3)*a(n-2)=0. - R. J. Mathar, Nov 17 2011
a(n) = binomial(2*n,n)/(n+1) * (2^(n+1) + (-1)^n)/3.
From Peter Bala, Aug 17 2021: (Start)
G.f.: A(x) = (sqrt(1 + 4*x) - sqrt(1 - 8*x))/(6*x).
A(x) = 1/sqrt(1 + 4*x)*c( 3*x/(1 + 4*x) ), where c(x) = (1 - sqrt(1- 4*x))/(2*x) is the g.f. of the Catalan numbers A000108. Cf. A151374.
In general, [x^n] ( 1/sqrt(1 + 4*x)*c( k*x/(1 + 4*x) ) ) = Catalan(n)*((k-1)^(n+1) + (-1)^(n+1))/k.
A(x) = 1/sqrt(1 - 8*x)*c( -3*x/(1 - 8*x) ). (End)
G.f. A(x) satisfies A(x) = sqrt( 1 + 2*x*A(x)^2 + 9*x^2*A(x)^4 ). - Paul D. Hanna, Dec 14 2024

Extensions

Typo in Name corrected by Peter Bala, Aug 17 2021
Previous Showing 21-30 of 721 results. Next