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.

User: Raul Prisacariu

Raul Prisacariu's wiki page.

Raul Prisacariu has authored 12 sequences. Here are the ten most recent ones:

A383873 a(n) = 3*a(n-1) - 2*a(n-2) + 5*a(n-3) starting with 1, 2, 3.

Original entry on oeis.org

1, 2, 3, 10, 34, 97, 273, 795, 2324, 6747, 19568, 56830, 165089, 479447, 1392313, 4043490, 11743079, 34103822, 99042758, 287636025, 835341669, 2425966747, 7045397028, 20460965935, 59421937484, 172570865722, 501173551873, 1455488611595, 4226973059649
Offset: 0

Author

Raul Prisacariu, May 18 2025

Keywords

Comments

The sequence appears as an example of recurring series in "A Mathematical and Philosophical Dictionary" by Charles Hutton.

Programs

  • Magma
    I:=[ 1, 2, 3]; [n le 3 select I[n] else 3*Self(n-1)-2*Self(n-2)+5*Self(n-3): n in [1..30]]; // Vincenzo Librandi, May 21 2025
  • Mathematica
    LinearRecurrence[{3,-2,5},{1,2,3},30] (* Vincenzo Librandi, May 21 2025 *)

Formula

G.f.: (x^2+x-1)/(5*x^3-2*x^2+3*x-1). - Alois P. Heinz, May 19 2025

A371201 a(n) = Sum_{k=prime(n)..prime(n+1)-1} k, with a(0) = 1.

Original entry on oeis.org

1, 2, 7, 11, 34, 23, 58, 35, 82, 153, 59, 201, 154, 83, 178, 297, 333, 119, 381, 274, 143, 453, 322, 513, 740, 394, 203, 418, 215, 442, 1673, 514, 801, 275, 1435, 299, 921, 957, 658, 1017, 1053, 359, 1855, 383, 778, 395, 2454, 2598, 898, 455, 922, 1413, 479, 2455, 1521, 1557, 1593
Offset: 0

Author

Raul Prisacariu, Mar 15 2024

Keywords

Comments

The sequence can be obtained graphically using the following grid walk rules. From an origin the first movement iteration consists of moving 1 unit in any direction. The n-th movement iteration consists of moving in the same direction n units. If n is a prime number, the movement iteration consists of first changing the movement direction by 90 degrees and then moving n units in the new direction. If n is a nonprime number, the movement iteration consists of moving n units in the same direction as the previous movement iteration. The sequence is obtained by measuring the length of each 90-degree turn.
a(0) is the length of the grid segment before doing any 90-degree turns and a(1) is the length of the first 90-degree turn.

Examples

			a(0) = 1.
a(1) = 2.
a(2) = 3 + 4 = 7.
a(3) = 5 + 6 = 11.
a(4) = 7 + 8 + 9 + 10 = 34.
a(5) = 11 + 12 = 23.
a(6) = 13 + 14 + 15 + 16 = 58.
a(7) = 17 + 18 = 35.
The natural numbers are summed in groups where each prime begins a new group,
  primes     v   v       v       v
         1   2   3   4   5   6   7   8   9  10  ...
        \-/ \-/ \-----/ \-----/ \-------------/
  a(n) = 1   2     7       11          34
    n  = 0   1     2       3           4
		

Crossrefs

Cf. A008837 (partial sums).

Programs

  • Maple
    ithprime(0):=1:
    a:= n-> ((j, k)-> (k-1+j)*(k-j)/2)(map(ithprime, [n, n+1])[]):
    seq(a(n), n=0..56);  # Alois P. Heinz, Mar 16 2024
  • Mathematica
    Join[{1},Table[Prime[n]+(Prime[n+1]+Prime[n])*(Prime[n+1]-Prime[n]-1)/2,{n,56}]] (* James C. McMahon, Apr 20 2024 *)
  • PARI
    first(n) = {
    	my(res = primes(n), t = 0);
    	for(i = 1, n,
    		res[i] = binomial(res[i],2) - t;
    		t+=res[i];
    	);
    	res	
    } \\ David A. Corneth, Mar 16 2024
    
  • Python
    from sympy import nextprime, prime
    def A371201(n):
        if n == 0: return 1
        q = nextprime(p:=prime(n))
        return (q-p)*(p+q-1)>>1 # Chai Wah Wu, Jun 01 2024

Formula

For n > 0, a(n) = A138383(n) - (prime(n+1) - prime(n)).
a(n) = binomial(prime(n+1), 2) - Sum_{k=0..n-1} a(k). - David A. Corneth, Mar 15 2024
a(n) = prime(n) + A054265(n), for n >= 1. - Michel Marcus, Mar 15 2024
a(n) = (prime(n+1)-prime(n))*(prime(n+1)+prime(n)-1)/2 for n>=1. - Chai Wah Wu, Jun 01 2024

Extensions

More terms from Michel Marcus, Mar 15 2024

A370491 The numerators of a series that converges to the Omega constant (A030178) obtained using Whittaker's root series formula.

Original entry on oeis.org

1, 1, -1, -5, 19, -3, -10187, 146847, 3268961, -211632497, 393324007, 5402916117, -3884618921299, -774402304798329, 148294948981707557, -3311395903665985169, -43463254022673425965, 14469962812566878696039, 6554498075974546253080309, -3074689522272735111427973673
Offset: 1

Author

Raul Prisacariu, Feb 19 2024

Keywords

Comments

Whittaker's root series formula is applied to 1 - 2x + x^2/2! - x^3/3! + x^4/4! - x^5/5! + x^6/6! - ..., which is the Taylor expansion of -x + e^(-x). We obtain the following infinite series that converges to the Omega constant (LambertW(1)): LambertW(1) = 1/2 + 1/14 - 1/259 - 5/9657 + 19/200187 - 3/18671081 ... . The sequence is formed by the numerators of the infinite series.

Examples

			a(1) is the numerator of -1/-2 = 1/2.
a(2) is the numerator of -(1/2)/((-2)*det ToeplitzMatrix((-2,1),(-2,1/2!))) = -(1/2)/((-2)*(7/2)) = 1/14.
a(3) is the numerator of -det ToeplitzMatrix((1/2!,-2),(1/2!,-1/3!))/(det ToeplitzMatrix((-2,1),(-2,1/2!))*det ToeplitzMatrix((-2,1,0),(-2,1/2!,-1/3!))) = -(-1/12)/((7/2)*(-37/6)) = -1/259.
		

Crossrefs

Cf. A030178, A370490 (denominator).

Formula

For n > 1, a(n) is the numerator of the simplified fraction -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n-1)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))), where c(0)=1, c(1)=-2, c(n) = (-1)^n/n!.

Extensions

a(9)-a(20) from Chai Wah Wu, Mar 23 2024

A370490 The denominators of a series that converges to the Omega constant (A030178) obtained using Whittaker's root series formula.

Original entry on oeis.org

2, 14, 259, 9657, 200187, 18671081, 7313976065, 1273374259615, 285038137030769, 79755360301275363, 9091712937155442435, 149243024021521700285, 1085736156475373087072485, 3071709182054627484879798019, 2005459027715242401528647218817, 1496371535371115486607560677791759
Offset: 1

Author

Raul Prisacariu, Feb 19 2024

Keywords

Comments

Whittaker's root series formula is applied to 1 - 2x + x^2/2! - x^3/3! + x^4/4! - x^5/5! + x^6/6! - ..., which is the Taylor expansion of -x + e^(-x). We obtain the following infinite series that converges to the Omega constant (LambertW(1)): LambertW(1) = 1/2 + 1/14 - 1/259 - 5/9657 + 19/200187 - 3/18671081 ... . The sequence is formed by the denominators of the infinite series.

Examples

			a(1) is the denominator of -1/-2 = 1/2.
a(2) is the denominator of -(1/2)/((-2)*det ToeplitzMatrix((-2,1),(-2,1/2!))) = -(1/2)/((-2)*(7/2)) = 1/14.
a(3) is the denominator of -det ToeplitzMatrix((1/2!,-2),(1/2!,-1/3!))/(det ToeplitzMatrix((-2,1),(-2,1/2!))*det ToeplitzMatrix((-2,1,0),(-2,1/2!,-1/3!))) = -(-1/12)/((7/2)*(-37/6)) = -1/259.
		

Crossrefs

Cf. A030178, A370491 (numerator).

Formula

for n>1, a(n) is the denominator of the simplified fraction -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n-1)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))), where c(0)=1, c(1)=-2, c(n) = (-1)^n/n!.

Extensions

a(9)-a(16) from Chai Wah Wu, Mar 23 2024

A369187 The numerators of a series that converges to the Dottie Number (A003957).

Original entry on oeis.org

1, -1, 1, -3, 1, 205, -4439, 111021, -1724351, 2074717, 2567577481, -246042951203, 14444487376705, -726562139423955, 1473171168838825, 1178164765176836393, -204468301714665778099, 138848947223110087743421, -11701779801284441802592247, 7774256876827576332115737
Offset: 1

Author

Raul Prisacariu, Jan 15 2024

Keywords

Comments

Whittaker's root series formula is applied to 1 - x - x^2/2! + x^4/4! - x^6/6! + ..., which is the Taylor expansion of cos(x) - x. The following infinite series for the Dottie number (D) is obtained: D = 1/1 - 1/3 + 1/12 - 3/260 + 1/5720 + 205/314248 - 4439/17255072 ... . The sequence is formed by the numerators of the series.

Examples

			a(1) is the numerator of -1/-1 = 1/1.
a(2) is the numerator of simplified -(-1/2!)/(-1* det ToeplitzMatrix((-1,1),(-1,-1/2!))) = (1/2)/(-3/2) = -1/3.
a(3) is the numerator of the simplified -det ToeplitzMatrix((-1/2!,-1),(-1/2!,0))/(det ToeplitzMatrix((-1,1),(-1,-1/2!))*det ToeplitzMatrix((-1,1,0),(-1,-1/2!,0))) = -(1/4)/((3/2)*-2) = 1/12.
		

Crossrefs

Cf. A003957.

Formula

a(1) = 1; for n > 1, a(n) is the numerator of the simplified fraction -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n+1)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n+1)))), where c(0)=1, c(1)=-1, c(2)=-1/2!, c(3)=0, c(4)=1/4!, c(5)=0, c(6)=-1/6!, and c(n) is the coefficient of x^n in the Taylor expansion of cos(x)-x.

Extensions

a(8)-a(20) from Chai Wah Wu, Feb 10 2024

A369186 The denominators of a series that converges to the Dottie Number (A003957).

Original entry on oeis.org

1, 3, 12, 260, 5720, 314248, 17255072, 1769058016, 181357735680, 29880655637760, 4923158441956352, 1189676108826729472, 287484053261423565824, 95784714773484796761088, 31913810779214031287095296, 2804341960426298188743438336, 1232120770958699233546743119872
Offset: 1

Author

Raul Prisacariu, Jan 15 2024

Keywords

Comments

Whittaker's root series formula is applied to 1 - x - x^2/2! + x^4/4! - x^6/6! + ..., which is the Taylor expansion of cos(x) - x. The following infinite series for the Dottie number (D) is obtained: D = 1/1 - 1/3 + 1/12 - 3/260 + 1/5720 + 205/314248 - 4439/17255072 ... . The sequence is formed by the denominators of the series.

Examples

			a(1) is the denominator of -1/-1 = 1/1.
a(2) is the denominator of simplified -(-1/2!)/(-1* det ToeplitzMatrix((-1,1),(-1,-1/2!))) = (1/2)/(-3/2) = -1/3.
a(3) is the denominator of the simplified -det ToeplitzMatrix((-1/2!,-1),(-1/2!,0))/(det ToeplitzMatrix((-1,1),(-1,-1/2!))*det ToeplitzMatrix((-1,1,0),(-1,-1/2!,0))) = -(1/4)/((3/2)*-2) = 1/12.
		

Crossrefs

Cf. A003957.

Formula

a(1)=1;
for n > 1, a(n) is the denominator of the simplified fraction -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n+1)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n+1)))), where c(0)=1, c(1)=-1, c(2)=-1/2!, c(3)=0, c(4)=1/4!, c(5)=0, c(6)=-1/6!, and c(n) is the coefficient of x^n in the Taylor expansion of cos(x)-x.

Extensions

a(8)-a(17) from Chai Wah Wu, Feb 10 2024

A368862 Numerators of an infinite series that converges to the negative inverse of Backhouse's constant (A088751).

Original entry on oeis.org

-1, -3, 1, 1, -1, 5, -19, -9, 41, -103, 17, 289, -169, 331, -689, -4991, 3999, 7833, -6509, 21827, -22165, -87637, 119441, -190981, -152513, 1482023, -425985, -1045091, 1071237, -14108791, 5845271, 39852203, -35832801, 54451699, 44061359, -435442725, 261309855, -22217917
Offset: 1

Author

Raul Prisacariu, Jan 08 2024

Keywords

Comments

Whittaker's root series formula is applied to 1 + Sum_{k>=1} prime(k) x^k. The following infinite series that converges to the negative inverse of Backhouse's constant (-x) is obtained:
x = -1/(1*2) - 3/(2*1) + 1/(1*1) + 1/(1*2) - 1/(2*3) + 5/(3*7) - 19/(7*10) - 9/(10*13) + 41/(13*21) - 103/(21*26) + 17/(26*33) + 289/(33*53) ...
The denominators of the infinite series are obtained by multiplying the absolute values of 2 consecutive terms from the sequence A030018.

Examples

			a(1) = -1;
a(2) = -3;
a(3) = -det ToeplitzMatrix((3,2),(3,5)) = 1;
a(4) = -det ToeplitzMatrix((3,2,1),(3,5,7)) = 1;
a(5) = -det ToeplitzMatrix((3,2,1,0),(3,5,7,11)) = -1;
a(6) = -det ToeplitzMatrix((3,2,1,0,0),(3,5,7,11,13)) = 5;
a(7) = -det ToeplitzMatrix((3,2,1,0,0,0),(3,5,7,11,13,17)) = -19.
		

Crossrefs

Formula

a(1) = -1.
For n > 1, a(n) = -det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n))), where c(0)=1 and c(n) is the n-th prime number.

Extensions

a(21)-a(38) from Stefano Spezia, Jan 09 2024

A368205 a(n) = 3*a(n-1) - 2*a(n-2) - a(n-3), with a(0)=1, a(1)=3 and a(2)=7.

Original entry on oeis.org

1, 3, 7, 14, 25, 40, 56, 63, 37, -71, -350, -945, -2064, -3952, -6783, -10381, -13625, -13330, -2359, 33208, 117672, 288959, 598325, 1099385, 1812546, 2640543, 3197152, 2497824, -1541375, -12816925, -37865849, -86422322, -170718343, -301444536, -476474600, -655816385, -713055419, -351058887, 1028750562, 4501424879, 11797832400, 25361896880, 47988600961
Offset: 0

Author

Raul Prisacariu, Dec 18 2023

Keywords

Comments

Whittaker's Root Series Formula is applied to the polynomial equation -1+2x+3x^2+x^3. The following infinite series involving the Plastic Ratio (rho) is obtained: rho - 1 = 1/2 - 3/(2*7) + 7/(7*21) - 14/(21*65) + 25/(65*200) - 40/(200*616) + 56/(616*1897) - ...
The terms of the sequence appear in the numerators of the infinite sequence (with alternating signs). The denominators of the sequence are formed by multiplying consecutive terms from the sequence A218836.

Examples

			a(0) = 1,
a(1) = 3*a(0) = 3*1 = 3,
a(2) = 3*a(1) - 2*a(0) = 3*3 - 2*1 = 7,
a(3) = 3*a(2) - 2*a(1) - a(0) = 3*7 - 2*3 - 1 = 14.
		

Crossrefs

Cf. A218836 (denominator), A060006.

Programs

  • Maple
    a:=proc(n) local c1,c2,c3;
     option remember;
    c1:=3; c2:=2; c3:=1;
    if n=0 then 1
    elif n=1 then 3
    elif n=2 then 7
    else c1*a(n-1)-c2*a(n-2)-c3*a(n-3); fi;
    end; # N. J. A. Sloane, Dec 31 2023
    [seq(a(n),n=0..30)];

Formula

a(n) = 3*a(n-1) - 2*a(n-2) - a(n-3).
a(n) = determinant of the n X n Toeplitz Matrix((3,2,-1,0,0,...,0),(3,1,0,0,0,...,0)).

A367597 The numerators of a series that converges to log(2) obtained using Whittaker's Root Series Formula.

Original entry on oeis.org

1, -1, 1, 1, -7, -13, 115, 5657, -50759, -2129735, 14303129, 567824371, -668626477, -2536766233351, -22685437440167, 6386546752479769, 164094712558603577, -8391397652598907629, -441809873725219477581, 29040435128150468206405, 2814195975064870847100773
Offset: 1

Author

Raul Prisacariu, Nov 24 2023

Keywords

Comments

The Whittaker's root series formula is applied to -1 + x + x^2/2! + x^3/3! + x^4/4! + x^5/5! + x^6/6! + ..., which is the Taylor expansion of e^x with the first coefficient having a negative sign (-1 instead of 1). We obtain log(2) = 1 - 1/3 + 1/39 + 1/975 - 7/40575 - 13/844501 + 115/73824373 + 5657/25814174655 .... The sequence is formed by the numerators of the series.

Examples

			a(1) is the numerator of -(-1)/1=1/1
a(2) is the numerator of -(-1)^2*(1/2!)/(1*det((1,1/2!),(-1,1)))=-(1/2)/(1*(3/2))=-1/3
a(3) is the numerator of -(-1)^3*det((1/2!,1/3!),(1,1/2!))/(det((1,1/2!),(-1,1))*det((1,1/2!,1/3!),(-1,1,1/2!),(0,-1,1)))=(1/12)/((3/2)*(13/6))=1/39
		

Crossrefs

Cf. A002162, A365595, A367596 (denominators).

Programs

  • Mathematica
    c[k_] := If[k < 0, 0, SeriesCoefficient[Exp[x] - 2, {x, 0, k}]]; Join[{1}, Table[(-1)^n*Det[ToeplitzMatrix[Table[c[3 - j], {j, 1, n}], Table[c[j + 1], {j, 1, n}]]] / (Det[ToeplitzMatrix[Table[c[2 - j], {j, 1, n}], Table[c[j], {j, 1, n}]]] * Det[ToeplitzMatrix[Table[c[2 - j], {j, 1, n + 1}], Table[c[j], {j, 1, n + 1}]]]), {n, 1, 20}] // Numerator] (* Vaclav Kotesovec, Nov 26 2023 *)

Formula

a(n) is the numerator of the simplified fraction -(-1)^n*det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n+1)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n+1)))), where c(0)=-1, c(1)=1, c(2)=1/2!, c(3)=1/3!, c(4)=1/4!,c(n)=1/n!.

Extensions

More terms from Vaclav Kotesovec, Nov 26 2023

A367596 The denominators of a series that converges to log(2) obtained using Whittaker's root series formula.

Original entry on oeis.org

1, 3, 39, 975, 40575, 844501, 73824373, 25814174655, 3868475107935, 724655165594943, 165910226233669599, 15194097535426090645, 4933425635511640104565, 5606480381963363479902783, 2450522415523358900846598879, 1224105922303030827661963930815, 693005978151926719613680243125855
Offset: 1

Author

Raul Prisacariu, Nov 24 2023

Keywords

Comments

The Whittaker's root series formula is applied to -1 + x + x^2/2! + x^3/3! + x^4/4! + x^5/5! + x^6/6! + ..., which is the Taylor expansion of e^x with the first coefficient having a negative sign (-1 instead of 1). We obtain log(2) = 1 - 1/3 + 1/39 + 1/975 - 7/40575 - 13/844501 + 115/73824373 + 5657/25814174655 .... The sequence is formed by the denominators of the series.

Examples

			a(1) is the denominator of -(-1)/1 = 1/1.
a(2) is the denominator of -(-1)^2*(1/2!)/(1*det((1,1/2!),(-1,1))) = -(1/2)/(1*(3/2)) = -1/3.
a(3) is the denominator of -(-1)^3*det((1/2!,1/3!),(1,1/2!))/(det((1,1/2!),(-1,1))*det((1,1/2!,1/3!),(-1,1,1/2!),(0,-1,1))) = (1/12)/((3/2)*(13/6)) = 1/39.
		

Crossrefs

Cf. A002162, A365594, A367597 (numerators).

Programs

  • Mathematica
    c[k_] := If[k < 0, 0, SeriesCoefficient[Exp[x] - 2, {x, 0, k}]]; Join[{1}, Table[(-1)^n*Det[ToeplitzMatrix[Table[c[3 - j], {j, 1, n}], Table[c[j + 1], {j, 1, n}]]] / (Det[ToeplitzMatrix[Table[c[2 - j], {j, 1, n}], Table[c[j], {j, 1, n}]]] * Det[ToeplitzMatrix[Table[c[2 - j], {j, 1, n + 1}], Table[c[j], {j, 1, n + 1}]]]), {n, 1, 20}] // Denominator] (* Vaclav Kotesovec, Nov 26 2023 *)

Formula

a(n) is the denominator of the simplified fraction -(-1)^n*det ToeplitzMatrix((c(2),c(1),c(0),0,0,...,0),(c(2),c(3),c(4),...,c(n+1)))/(det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n)))*det ToeplitzMatrix((c(1),c(0),0,...,0),(c(1),c(2),c(3),...,c(n+1)))), where c(0)=-1, c(1)=1, c(2)=1/2!, c(3)=1/3!, c(4)=1/4!, c(n)=1/n!.

Extensions

More terms from Vaclav Kotesovec, Nov 26 2023