A133058 -id:A133058 - cp's OEIS frontend

A381466 a(0) = 4; for n > 0, a(n) = a(n-1) + n if G = 1 or a(n) = n/G if G > 1, where G = gcd(a(n-1), n).

4, 5, 7, 10, 2, 7, 13, 20, 2, 11, 21, 32, 3, 16, 7, 22, 8, 25, 43, 62, 10, 31, 53, 76, 6, 31, 57, 9, 37, 66, 5, 36, 8, 41, 75, 7, 43, 80, 19, 58, 20, 61, 103, 146, 22, 67, 113, 160, 3, 52, 25, 76, 13, 66, 9, 64, 7, 64, 29, 88, 15, 76, 31, 94, 32, 97, 163, 230, 34, 103, 173, 244

Offset: 0

Sam Chapman, Feb 24 2025

nonn

If a(n) < n for some n, then a(n+1) > n+1.
If a(n) > n, a(n+1) > n+1, and a(n+2) > n+2 for some n, then a(n+3) < n+3.
1 < a(n) for all n.
sqrt(n/6) < a(n) <= 7n/2 - 9/2 for all n.
a(p)>p for all primes p.
If one were to use the same rule to generate this sequence with any other initial value that is congruent to 4 or 8 (mod 12), that sequence would agree with this one for all n>3.
If one were to use the same rule to generate this sequence with an initial term that is not congruent to 4 or 8 (mod 12), then it would output the number 1 before the 5th term. When a sequence follows a(n)’s rules and outputs the number 1 at some index k, one gets the following quasi-periodic behavior: 1, k+2, 1, k+4, 1, k+6, etc., and are as such “boring” sequences.

			a(12) = 3 and gcd(3, 13) = 1, so a(13) = 3 + 13 = 16.  gcd(16, 14) = 2, so a(14) = 14/2 = 7.

Sam Chapman, Table of n, a(n) for n = 0..10000

Similar to A133058, A091508.

s={4};Do[G=GCD[s[[-1]],n];AppendTo[s,If[G==1,s[[-1]]+n,n/G]],{n,71}];s (* James C. McMahon, Mar 02 2025 *)

lista(nn) = my(v = vector(nn)); v[1] = 4; for (n=2, nn, my(g=gcd(v[n-1], n-1)); if (g==1, v[n] = v[n-1] + n-1, v[n] = (n-1)/g);); v; \\ Michel Marcus, Feb 26 2025

A262922 a(1)=1; for n>1, a(n) = a(n-1) + n + 2 if a(n-1) and n are coprime, otherwise a(n) = a(n-1)/gcd(a(n-1),n).

Original entry on oeis.org

1, 5, 10, 5, 1, 9, 18, 9, 1, 13, 26, 13, 1, 17, 34, 17, 1, 21, 42, 21, 1, 25, 50, 25, 1, 29, 58, 29, 1, 33, 66, 33, 1, 37, 74, 37, 1, 41, 82, 41, 1, 45, 90, 45, 1, 49, 98, 49, 1, 53, 106, 53, 1, 57, 114, 57, 1, 61, 122, 61, 1, 65, 130, 65, 1, 69, 138, 69, 1, 73, 146, 73, 1, 77, 154, 77, 1, 81, 162

Offset: 1

Ctibor O. Zizka, Oct 04 2015

nonn

This recurrence is quasi-periodic.
For some choice of starting value a(1) there exists an integer t>=1 such that a(4*t-3)=1, a(4*t-2)=4*t+1, a(4*t-1)=2*(4*t+1), a(4*t)=4*t+1. The loop is (1,x,2x,x).
For some choice of starting value a(1) there exists an integer t>=1 such that a(2*t)=2*t-1 and a(2*t-1)=2*(2*t-1). The loop is (x,2x). See also A133058.
Quasi-periodic sequences exist only for R=0,1,2 or 3 in a(n) = a(n-1) + n + R. For R=0,1,2 all starting values give a quasi-periodic sequence. The respective loop is (1,x) for R=0, (1,x,2x,2) for R=1, (1,x,2x,x) or (x,2x) for R=2. For R=3 only some starting values converge to a 6-loop (4x+2,2x+1,3x+6,x+2,2x+9,3x+17). Conjecture: For R>=4 the recurrence is not quasi-periodic.

Benoit Cloitre, 10 conjectures in additive number theory, arXiv:1101.4274 [math.NT], 2011.
Eric S. Rowland, A natural prime-generating recurrence, arXiv:0710.3217 [math.NT], 2007-2008.

Cf. A091508, A106108, A133058, A133579, A133580, A255051, A255140.

a[1] = 1; a[n_] := a[n] = If[CoprimeQ[a[n - 1], n], a[n - 1] + n + 2, a[n - 1]/GCD[a[n - 1], n]]; Array[a, {79}] (* Michael De Vlieger, Oct 05 2015 *)

A=vector(1000, i, 1); for(n=2, #A, A[n]=if(gcd(A[n-1], n)>1, A[n-1]/gcd(A[n-1], n), A[n-1]+n+2))

Maple suggests the rational o.g.f. (-x^6 - x^5 - x^3 + 6x^2 + 4x + 1)/((x + 1)(x - 1)^2(x^2 + 1)^2), which should be easy to check. - Pater Bala, Oct 04 2015

A264767 a(1)=1; for n>1, a(n) = a(n-1) + n if x=0, otherwise a(n) = a(n-1) / 2^x, where x is the exponent of highest power of 2 dividing gcd(a(n-1),n).

Original entry on oeis.org

1, 3, 6, 3, 8, 4, 11, 19, 28, 14, 25, 37, 50, 25, 40, 5, 22, 11, 30, 15, 36, 18, 41, 65, 90, 45, 72, 18, 47, 77, 108, 27, 60, 30, 65, 101, 138, 69, 108, 27, 68, 34, 77, 121, 166, 83, 130, 65, 114, 57, 108, 27, 80, 40, 95, 151, 208, 104, 163, 223, 284, 142, 205, 269, 334, 167, 234, 117, 186, 93, 164, 41, 114, 57, 132, 33, 110, 55, 134, 67, 148, 74, 157, 241, 326, 163, 250, 125, 214, 107, 198, 99, 192, 96, 191, 287, 384, 192, 291, 391, 492, 246

Offset: 1

Ctibor O. Zizka, Nov 23 2015

nonn

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A007814, A133058.

nxt[{n_,a_}]:=Module[{x=IntegerExponent[GCD[a,n+1],2]},{n+1,If[x== 0,a+n+1,a/2^x]}]; NestList[nxt,{1,1},110][[All,2]]

A309665 a(1)=1; for n > 1, a(n) = a(n-1)/gcd(a(n-1),n) + n + 1.

Original entry on oeis.org

1, 4, 8, 7, 13, 20, 28, 16, 26, 24, 36, 16, 30, 30, 18, 26, 44, 41, 61, 82, 104, 75, 99, 58, 84, 69, 51, 80, 110, 42, 74, 70, 104, 87, 123, 78, 116, 97, 137, 178, 220, 153, 197, 242, 288, 191, 239, 288, 338, 220, 272, 121, 175, 230, 102, 108, 94, 106, 166

Offset: 1

Dennis Reichard, Aug 11 2019

n is a lower bound on a(n), furthermore n+3 is a lower bound if n > 2. This can easily be proved by induction. It appears that both the average value and the upper bound grow either linearly or slightly faster than linearly.

			a(4) = a(3)/gcd(a(3),4) + 4 + 1 = 8/gcd(8,4) + 5 = 8/4 + 5 = 2 + 5 = 7.

Seiichi Manyama, Table of n, a(n) for n = 1..10000

Cf. A133058.

[n le 1 select 1 else  Self(n-1)/Gcd(Floor(Self(n-1)),n) + n + 1 : n in [1..60]]; // Marius A. Burtea, Aug 11 2019

a[1] = 1; a[n_] := a[n] = a[n-1]/GCD[a[n - 1], n] + n + 1; Array[a, 60] (* Amiram Eldar, Aug 14 2019 *)

A322558 a(0)=1, a(1)=1; for n>1, a(n)=a(n-1)+a(n-2) if a(n-1) is less than or equal to n-1, otherwise a(n)=a(n-1)-(n-1).

Original entry on oeis.org

1, 1, 2, 3, 5, 1, 6, 7, 13, 5, 18, 8, 26, 14, 1, 15, 16, 31, 14, 45, 26, 6, 32, 10, 42, 18, 60, 34, 7, 41, 12, 53, 22, 75, 42, 8, 50, 14, 64, 26, 90, 50, 9, 59, 16, 75, 30, 105, 58, 10, 68, 18, 86, 34, 120, 66, 11, 77, 20, 97, 38, 135, 74, 12, 86, 22, 108, 42, 150, 82, 13, 95, 24, 119, 46, 165, 90, 14, 104, 26

Offset: 0

Jackson Haselhorst, Aug 28 2019

The graph of the sequence appears random until n>16, after which the graph creates seven distinct lines.

Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,2,0,0,0,0,0,0,-1).

Cf. A133058, A380820.

a[0] = a[1] = 1; a[n_] := a[n] = If[a[n - 1] <= n - 1, a[n - 1] + a[n - 2], a[n - 1] - n + 1]; Array[a, 100, 0] (* Amiram Eldar, Aug 29 2019 *)

Vec((1 + x + 2*x^2 + 3*x^3 + 5*x^4 + x^5 + 6*x^6 + 5*x^7 + 11*x^8 + x^9 + 12*x^10 - 2*x^11 + 24*x^12 + 2*x^13 - 12*x^14 - 10*x^15 + 8*x^16 - 2*x^17 + 3*x^18 - 6*x^19 + 4*x^20 + 11*x^21 + 15*x^22 - 17*x^23 - 2*x^24 - 2*x^25 - 4*x^26 - 4*x^27 - 4*x^28 - 8*x^29 + 8*x^30) / ((1 - x)^2*(1 + x + x^2 + x^3 + x^4 + x^5 + x^6)^2) + O(x^40)) \\ Colin Barker, Aug 29 2019

For n>16, the sequence follows a pattern of seven, and each term lies on one of the following lines:
If n is of the form 7k+3, then a(n) = (11/7)n+(30/7);
if n is of the form 7k+4, then a(n) = (4/7)n+(26/7);
if n is of the form 7k+5, then a(n) = (15/7)n+(30/7);
if n is of the form 7k+6, then a(n) = (8/7)n+(22/7);
if n is of the form 7k,   then a(n) = (1/7)n+3;
if n is of the form 7k+1, then a(n) = (9/7)n+(26/7);
if n is of the form 7k+2, then a(n) = (2/7)n+(24/7).
From Colin Barker, Aug 29 2019: (Start)
G.f.: (1 + x + 2*x^2 + 3*x^3 + 5*x^4 + x^5 + 6*x^6 + 5*x^7 + 11*x^8 + x^9 + 12*x^10 - 2*x^11 + 24*x^12 + 2*x^13 - 12*x^14 - 10*x^15 + 8*x^16 - 2*x^17 + 3*x^18 - 6*x^19 + 4*x^20 + 11*x^21 + 15*x^22 - 17*x^23 - 2*x^24 - 2*x^25 - 4*x^26 - 4*x^27 - 4*x^28 - 8*x^29 + 8*x^30) / ((1 - x)^2*(1 + x + x^2 + x^3 + x^4 + x^5 + x^6)^2).
a(n) = 2*a(n-7) - a(n-14) for n>30.
(End)

A334943 a(1) = 1, a(n) = a(n-1) / gcd(a(n-1),n) if this gcd is > 1, else a(n) = 3*a(n-1) + n + 1.

Original entry on oeis.org

1, 6, 2, 1, 9, 3, 17, 60, 20, 2, 18, 3, 23, 84, 28, 7, 39, 13, 59, 198, 66, 3, 33, 11, 59, 204, 68, 17, 81, 27, 113, 372, 124, 62, 222, 37, 1, 42, 14, 7, 63, 3, 53, 204, 68, 34, 150, 25, 125, 5, 67, 254, 816, 136, 464, 58, 232, 4, 72, 6, 80, 40, 184, 23, 135

Offset: 1

Ctibor O. Zizka, May 17 2020

nonn

A variant of A133058. The behavior of simple computational models of the form a(1), a(n) = a(n-1) / gcd(a(n-1),n) if this gcd is > 1, else a(n) = X*a(n-1) + Y*n + R, depending on parameters [X, Y, R], shows Wolfram complexity classes for cellular automata.

			a(2) = 3*a(1) + 2 + 1 = 6, a(3) = a(2)/3 = 2, a(4) = a(3)/2 = 1, a(5) = 3*a(4) + 5 + 1 = 9, ...

Robert Israel, Table of n, a(n) for n = 1..10000

Cf. A133058.

a:=[1]; for n in [2..70] do if Gcd(a[n-1], n) eq 1 then Append(~a, 3* a[n-1]+n+1); else Append(~a, a[n-1] div Gcd(a[n-1], n)); end if; end for; a; // Marius A. Burtea, May 17 2020

N:= 100: # for a(1)..a(N)
V:= Vector(N):
V[1]:= 1:
for n from 2 to N do
  g:= igcd(V[n-1],n);
  if g > 1 then V[n]:= V[n-1]/g else V[n]:= 3*V[n-1]+n+1 fi
od:
convert(V,list); # Robert Israel, Jun 22 2020

a[1] = 1; a[n_] := a[n] = If[(g = GCD[a[n-1], n]) > 1, a[n-1]/g, 3*a[n-1] + n + 1]; Array[a, 100]
nxt[{n_,a_}]:=With[{c=GCD[a,n+1]},{n+1,If[c>1,a/c,3a+n+2]}]; NestList[nxt,{1,1},70][[;;,2]] (* Harvey P. Dale, May 14 2024 *)

lista(nn) = {my(va = vector(nn)); va[1] = 1; for (n=2, nn, my(g = gcd(va[n-1], n)); if (g > 1, va[n] = va[n-1]/g, va[n] = 3*va[n-1]+n+1);); va;} \\ Michel Marcus, May 17 2020

A327562 a(0) = a(1) = 1; for n > 1, a(n) = (a(n-1) + a(n-2)) / gcd(a(n-1), a(n-2)) if a(n-1) and a(n-2) are not coprime, otherwise a(n) = a(n-1) + a(n-2) + 1.

Original entry on oeis.org

1, 1, 3, 5, 9, 15, 8, 24, 4, 7, 12, 20, 8, 7, 16, 24, 5, 30, 7, 38, 46, 42, 44, 43, 88, 132, 5, 138, 144, 47, 192, 240, 9, 83, 93, 177, 90, 89, 180, 270, 5, 55, 12, 68, 20, 22, 21, 44, 66, 5, 72, 78, 25, 104, 130, 9, 140, 150, 29, 180, 210, 13, 224, 238, 33, 272, 306

Offset: 0

Ian Band, Sep 16 2019

nonn

The sequence increases rapidly after n = 92.
From roughly n = 480 to n = 600, the sequence increases relatively fast and is almost a perfect exponential function.
Redefining a(0) and a(1) can result in drastically different sequences.

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Cf. A133058.

a:=[1,1]; for n in [3..67] do  if Gcd(a[n-1],a[n-2]) ne 1 then Append(~a,(a[n-1]+a[n-2])/Gcd(a[n-1],a[n-2])); else Append(~a,a[n-1]+a[n-2]+1); end if; end for; a; // Marius A. Burtea, Sep 19 2019

a[0]=a[1]=1; a[n_] := a[n] = Block[{g = GCD[a[n-1], a[n-2]]}, If[g==1,
a[n-1] + a[n-2] + 1, (a[n-1] + a[n-2])/g]]; Array[a, 67, 0] (* Giovanni Resta, Sep 19 2019 *)
nxt[{a_,b_}]:={b,If[!CoprimeQ[a,b],(a+b)/GCD[a,b],a+b+1]}; NestList[nxt,{1,1},70][[;;,1]] (* Harvey P. Dale, Feb 14 2024 *)

import math
def a(n): # Iteratively generates an array containing the first n terms of a(n), n should be greater than 2
    a1 = 1 # this will hold a(n-1), its initial value is a(1)
    a2 = 1 # this will hold a(n-2), its initial value is a(0)
    terms = [None] * n
    terms[0] = a2
    terms[1] = a1
    for i in range(2, n):
        gcdPrev2 = math.gcd(a1, a2)
        if(gcdPrev2 > 1):
            terms[i] = int((a1 + a2) / gcdPrev2)
        else:
            terms[i] = a1 + a2 + 1
        a2 = a1
        a1 = terms[i]
    return terms

a(0) = a(1) = 1; for n > 1, a(n) = (a(n-1) + a(n-2)) / gcd(a(n-1), a(n-2)) if gcd(a(n-1), a(n-2)) > 1, otherwise a(n) = a(n-1) + a(n-2) + 1.

A358787 a(1)=1; let x=gcd(a(n-1),n); for n > 1, a(n) = a(n-1) + n if x=1 or a(n-1)/x=1, otherwise a(n) = a(n-1)/x.

Original entry on oeis.org

1, 3, 6, 3, 8, 4, 11, 19, 28, 14, 25, 37, 50, 25, 5, 21, 38, 19, 38, 19, 40, 20, 43, 67, 92, 46, 73, 101, 130, 13, 44, 11, 44, 22, 57, 19, 56, 28, 67, 107, 148, 74, 117, 161, 206, 103, 150, 25, 74, 37, 88, 22, 75, 25, 5, 61, 118, 59, 118, 59, 120, 60, 20, 5, 70, 35, 102, 3, 72, 36

Offset: 1

Gary Yane, Nov 30 2022

nonn

			For n=2, gcd(2,1)=1 so a(2) = 2+1 = 3.
For n=3, gcd(3,3)=3=a(2) so a(3) = 3+3 = 6.
For n=4, gcd(4,6)=2 so a(4) = 6/2 = 3.

Michael De Vlieger, Log log scatterplot of a(n), n = 1..2^20.
Michael De Vlieger, Log log scatterplot of a(n), n = 1..2^16, with x = gcd(a(n-1), n), showing x=1 or a(n-1)/x = 1 in red, else dark blue.

Cf. A264767, A133058, A133579, A133580, A255051, A255140, A262922.

nn = 2^16; a[1] = 1; Do[g = GCD[a[n - 1], n]; If[Or[g == 1, Set[k, a[n - 1]/g] == 1], a[n] = a[n - 1] + n, a[n] = k], {n, 2, nn}]; Array[a, nn] (* Michael De Vlieger, Dec 13 2022 *)

from math import gcd
from itertools import count, islice
def agen(): # generator of terms
    an = 1
    for n in count(2):
        yield an
        x = gcd(an, n)
        an = an + n if x == 1 or x == an else an//x
print(list(islice(agen(), 70))) # Michael S. Branicky, Dec 15 2022

A372748 a(1) = 3; for n > 1, a(n) = a(n - 1) if GCD(n - 1, a(n - 1)) = 1, otherwise a(n) = n - 1 - a(n - 1) / GCD(n - 1, a(n - 1)).

Original entry on oeis.org

3, 3, 3, 2, 3, 3, 5, 5, 5, 5, 9, 9, 9, 9, 9, 12, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 25, 25, 25, 25, 25, 25, 25, 25, 25, 30, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 61, 61, 61, 61, 61, 61, 61, 61

Offset: 1

Ctibor O. Zizka, May 12 2024

nonn

a(n) = n/2 for n from {4,6,10,26,62,122,298,626,1094,2186,...}.

			a(1) = 3.
a(2) = 3 because GCD(1,3) = 1.
a(3) = 3 because GCD(2,3) = 1.
a(4) = 3 - 3/GCD(3,3) = 2.
and so on.

Paolo Xausa, Table of n, a(n) for n = 1..10000

Cf. A000040, A133058.

nxt[{n_,a_}]:={n+1,If[GCD[n,a]==1,a,n-a/GCD[n,a]]}; NestList[nxt,{1,3},70][[;;,2]] (* Harvey P. Dale, Feb 11 2025 *)
FoldList[If[CoprimeQ[#, #2], #, #2 - #/GCD[#, #2]] &, 3, Range[100]] (* Paolo Xausa, Feb 12 2025 *)

A381331 a(1) = a(2) = 1; for n > 2, a(n) = floor((n - 2)*a(n - 1)/a(n - 2)) + GCD(n - 2, a(n - 2)).

Original entry on oeis.org

1, 1, 2, 5, 8, 7, 5, 5, 8, 13, 15, 12, 9, 21, 31, 27, 14, 9, 11, 31, 54, 35, 16, 11, 16, 35, 55, 41, 21, 15, 21, 57, 85, 48, 19, 15, 28, 70, 93, 52, 24, 22, 38, 74, 84, 51, 30, 28, 44, 79, 88, 56, 33, 34, 55, 89, 144, 91, 39, 25, 38, 96, 155, 102, 42, 28, 44, 105, 160, 104

Offset: 1

Ctibor O. Zizka, Feb 20 2025

At n = 499 the sequence settles down and becomes quasi-periodic with a 6-loop. Empiricaly 3 >= a(n + 1)/a(n) >= 1/3. The system is sensitive to the choice of initial terms [a(1),a(2)]. Only some values of initial terms results in a 6-loop like this sequence, the vast majority of initial terms show a "noisy quasiperiodic" like structures in the plot. Trials made for [a(1), a(2)] from [1, 1] to [100, 100] and for n up to 70000. May it be the sequence converges to a 6-loop for some large enough n, independent on the choice of initial terms ?

			a(1) = 1
a(2) = 1
a(3) = floor(1*1/1) + GCD(1,1) = 2
a(4) = floor(2*2/1) + GCD(2,1) = 5
a(5) = floor(3*5/2) + GCD(3,2) = 8
and so on.

Ray Chandler, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,-1,1,-1,1,0,0,0,0,0,0,1,-1,1,-1,1,-1).

Cf. A133058, A145102.

a[n_] := a[n] = If[n < 3, 1, Floor[(n-2)*a[n-1]/a[n-2]] + GCD[n-2, a[n-2]]]; Array[a, 70] (* Amiram Eldar, Feb 20 2025 *)

For n >= 499:
if n mod 6 = 0, a(n) = 2*n - 1 + 2*((n/2) mod 2).
if n mod 6 = 1, a(n) = n + 2.
if n mod 6 = 2, a(n) = (n + 2)/2.
if n mod 6 = 3, a(n) = (n - 1)/2.
if n mod 6 = 4, a(n) = n - 2 - (n/2) mod 2.
if n mod 6 = 5, a(n) = 2*n - 6 + 3*((n + 1)/2 mod 2).

cp's OEIS Frontend

A381466 a(0) = 4; for n > 0, a(n) = a(n-1) + n if G = 1 or a(n) = n/G if G > 1, where G = gcd(a(n-1), n).

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Mathematica

PARI

A262922 a(1)=1; for n>1, a(n) = a(n-1) + n + 2 if a(n-1) and n are coprime, otherwise a(n) = a(n-1)/gcd(a(n-1),n).

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Mathematica

PARI

Formula

A264767 a(1)=1; for n>1, a(n) = a(n-1) + n if x=0, otherwise a(n) = a(n-1) / 2^x, where x is the exponent of highest power of 2 dividing gcd(a(n-1),n).

Views

Author

Keywords

Links

Crossrefs

Programs

Mathematica

A309665 a(1)=1; for n > 1, a(n) = a(n-1)/gcd(a(n-1),n) + n + 1.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Magma

Mathematica

A322558 a(0)=1, a(1)=1; for n>1, a(n)=a(n-1)+a(n-2) if a(n-1) is less than or equal to n-1, otherwise a(n)=a(n-1)-(n-1).

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Mathematica

PARI

Formula

A334943 a(1) = 1, a(n) = a(n-1) / gcd(a(n-1),n) if this gcd is > 1, else a(n) = 3*a(n-1) + n + 1.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Magma

Maple

Mathematica

PARI

A327562 a(0) = a(1) = 1; for n > 1, a(n) = (a(n-1) + a(n-2)) / gcd(a(n-1), a(n-2)) if a(n-1) and a(n-2) are not coprime, otherwise a(n) = a(n-1) + a(n-2) + 1.

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Magma

Mathematica

Python

Formula

A358787 a(1)=1; let x=gcd(a(n-1),n); for n > 1, a(n) = a(n-1) + n if x=1 or a(n-1)/x=1, otherwise a(n) = a(n-1)/x.

Views