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.

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A130487 a(n) = Sum_{k=0..n} (k mod 9) (Partial sums of A010878).

Original entry on oeis.org

0, 1, 3, 6, 10, 15, 21, 28, 36, 36, 37, 39, 42, 46, 51, 57, 64, 72, 72, 73, 75, 78, 82, 87, 93, 100, 108, 108, 109, 111, 114, 118, 123, 129, 136, 144, 144, 145, 147, 150, 154, 159, 165, 172, 180, 180, 181, 183, 186, 190, 195, 201, 208, 216, 216, 217, 219, 222, 226
Offset: 0

Views

Author

Hieronymus Fischer, May 31 2007

Keywords

Comments

Let A be the Hessenberg n X n matrix defined by A[1,j]=j mod 9, A[i,i]:=1, A[i,i-1]=-1. Then, for n >= 1, a(n)=det(A). - Milan Janjic, Jan 24 2010

Crossrefs

Programs

  • GAP
    a:=[0,1,3,6,10,15,21,28,36,36];; for n in [11..71] do a[n]:=a[n-1]+a[n-9]-a[n-10]; od; a; # G. C. Greubel, Aug 31 2019
  • Magma
    I:=[0,1,3,6,10,15,21,28,36,36]; [n le 10 select I[n] else Self(n-1) + Self(n-9) - Self(n-10): n in [1..71]]; // G. C. Greubel, Aug 31 2019
    
  • Maple
    seq(coeff(series(x*(1-9*x^8+8*x^9)/((1-x^9)*(1-x)^3), x, n+1), x, n), n = 0 .. 70); # G. C. Greubel, Aug 31 2019
  • Mathematica
    Accumulate[PadRight[{},120,Range[0,8]]] (* Harvey P. Dale, Dec 19 2018 *)
    Accumulate[Mod[Range[0,100],9]] (* Harvey P. Dale, Oct 16 2021 *)
  • PARI
    a(n) = sum(k=0, n, k % 9); \\ Michel Marcus, Apr 28 2018
    
  • Sage
    def A130487_list(prec):
        P. = PowerSeriesRing(ZZ, prec)
        return P(x*(1-9*x^8+8*x^9)/((1-x^9)*(1-x)^3)).list()
    A130487_list(70) # G. C. Greubel, Aug 31 2019
    

Formula

a(n) = 36*floor(n/9) + A010878(n)*(A010878(n) + 1)/2.
G.f.: (Sum_{k=1..8} k*x^k)/((1-x^9)*(1-x)).
G.f.: x*(1 - 9*x^8 + 8*x^9)/((1-x^9)*(1-x)^3).

A319704 Filter sequence which records for primes their residue modulo 4, and for all other numbers assigns a unique number.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 3, 7, 8, 9, 3, 10, 5, 11, 12, 13, 5, 14, 3, 15, 16, 17, 3, 18, 19, 20, 21, 22, 5, 23, 3, 24, 25, 26, 27, 28, 5, 29, 30, 31, 5, 32, 3, 33, 34, 35, 3, 36, 37, 38, 39, 40, 5, 41, 42, 43, 44, 45, 3, 46, 5, 47, 48, 49, 50, 51, 3, 52, 53, 54, 3, 55, 5, 56, 57, 58, 59, 60, 3, 61, 62, 63, 3, 64, 65, 66, 67, 68, 5, 69, 70, 71, 72, 73, 74, 75, 5, 76, 77, 78, 5, 79, 3
Offset: 1

Views

Author

Antti Karttunen, Sep 26 2018

Keywords

Comments

Restricted growth sequence transform of function f defined as f(n) = A010873(n) when n is a prime, otherwise -n.
For all i, j:
a(i) = a(j) => A010873(i) = A010873(j),
a(i) = a(j) => A305801(i) = A305801(j),
a(i) = a(j) => A319714(i) = A319714(j).

Crossrefs

Cf. A002145 (positions of 3's), A002144 (positions of 5's).
Cf. also A319350, A319705, A319706.

Programs

  • PARI
    up_to = 100000;
    rgs_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(om,invec[i]), my(pp = mapget(om, invec[i])); outvec[i] = outvec[pp] , mapput(om,invec[i],i); outvec[i] = u; u++ )); outvec; };
    A319704aux(n) = if(isprime(n),-(n%4),n);
    v319704 = rgs_transform(vector(up_to,n,A319704aux(n)));
    A319704(n) = v319704[n];

A053839 a(n) = (sum of digits of n written in base 4) modulo 4.

Original entry on oeis.org

0, 1, 2, 3, 1, 2, 3, 0, 2, 3, 0, 1, 3, 0, 1, 2, 1, 2, 3, 0, 2, 3, 0, 1, 3, 0, 1, 2, 0, 1, 2, 3, 2, 3, 0, 1, 3, 0, 1, 2, 0, 1, 2, 3, 1, 2, 3, 0, 3, 0, 1, 2, 0, 1, 2, 3, 1, 2, 3, 0, 2, 3, 0, 1, 1, 2, 3, 0, 2, 3, 0, 1, 3, 0, 1, 2, 0, 1, 2, 3, 2, 3, 0, 1, 3, 0, 1, 2, 0, 1, 2, 3, 1, 2, 3, 0, 3, 0, 1, 2, 0, 1, 2, 3, 1
Offset: 0

Views

Author

Henry Bottomley, Mar 28 2000

Keywords

Comments

a(n) is the third row of the array in A141803. - Andrey Zabolotskiy, May 16 2016
This is the fixed point of the morphism 0->0123, 1->1230, 2->2301, 3->3012 starting with 0. Let t be the (nonperiodic) sequence of positions of 0, and likewise, u for 1, v for 2, and w for 3; then t(n)/n -> 4, u(n)/n -> 4, v(n)/n -> 4, w(n)/n -> 4, and t(n) + u(n) + v(n) + w(n) = 16*n - 6 for n >= 1. - Clark Kimberling, May 31 2017

Examples

			First three iterations of the morphism 0->0123, 1->1230, 2->2301, 3->3012:
  0123
  0123123023013012
  0123123023013012123023013012012323013012012312303012012312302301
		

Crossrefs

Programs

  • Maple
    seq(convert(convert(n,base,4),`+`) mod 4, n=0..100); # Robert Israel, May 18 2016
  • Mathematica
    Mod[Total@ IntegerDigits[#, 4], 4] & /@ Range[0, 120] (* Michael De Vlieger, May 17 2016 *)
    s = Nest[Flatten[# /. {0 -> {0, 1, 2, 3}, 1 -> {1, 2, 3, 0}, 2 -> {2, 3, 0, 1}, 3 -> {3, 0, 1, 2}}] &, {0}, 9];   (* - Clark Kimberling, May 31 2017 *)
  • PARI
    a(n) = vecsum(digits(n,4)) % 4; \\ Michel Marcus, May 16 2016
    
  • PARI
    a(n) = sumdigits(n, 4) % 4; \\ Michel Marcus, Jul 04 2018

Formula

a(n) = A010873(A053737(n)). - Andrey Zabolotskiy, May 18 2016
G.f. G(x) satisfies x^81*G(x) - (x^72+x^75+x^78+x^81)*G(x^4) + (x^48+x^60+x^63-x^64+x^72+x^75-x^76+x^78-x^79-x^88-x^91-x^94)*G(x^16) + (-1+x^16-x^48-x^60-x^63+2*x^64+x^76+x^79-x^80+x^112+x^124+x^127-x^128-x^140-x^143)*G(x^64) + (1-x^16-x^64+x^80-x^256+x^272+x^320-x^336)*G(x^256) = 0. - Robert Israel, May 18 2016

A145768 a(n) = the bitwise XOR of squares of first n natural numbers.

Original entry on oeis.org

0, 1, 5, 12, 28, 5, 33, 16, 80, 1, 101, 28, 140, 37, 225, 0, 256, 33, 357, 12, 412, 37, 449, 976, 400, 993, 325, 924, 140, 965, 65, 896, 1920, 961, 1861, 908, 1692, 965, 1633, 912, 1488, 833, 1445, 668, 1292, 741, 2721, 512, 2816, 609, 2981, 396, 2844, 485
Offset: 0

Views

Author

Vladimir Reshetnikov, Oct 18 2008

Keywords

Comments

Up to n=10^8, a(15) is the only zero term and a(1)=a(9) are the only terms for which a(n)=1. Can it be proved that any number can only appear a finite number of times in this sequence? [M. F. Hasler, Oct 20 2008]
Even terms occur at A014601, odd terms at A042963; A010873(a(n))=A021913(n+1). - Reinhard Zumkeller, Jun 05 2012
If squares occur, they must be at indexes != 2 or 5 (mod 8). - Roderick MacPhee, Jul 17 2017

Crossrefs

Programs

  • Haskell
    import Data.Bits (xor)
    a145768 n = a145768_list !! n
    a145768_list = scanl1 xor a000290_list  -- Reinhard Zumkeller, Jun 05 2012
    
  • Maple
    A[0]:= 0:
    for n from 1 to 100 do A[n]:= Bits:-Xor(A[n-1],n^2) od:
    seq(A[i],i=0..100); # Robert Israel, Dec 08 2019
  • Mathematica
    Rest@ FoldList[BitXor, 0, Array[#^2 &, 50]]
  • PARI
    an=0; for( i=1,50, print1(an=bitxor(an,i^2),",")) \\ M. F. Hasler, Oct 20 2008
    
  • PARI
    al(n)=local(m);vector(n,k,m=bitxor(m,k^2))
    
  • Python
    from functools import reduce
    from operator import xor
    def A145768(n):
        return reduce(xor, [x**2 for x in range(n+1)]) # Chai Wah Wu, Aug 08 2014

Formula

a(n)=1^2 xor 2^2 xor ... xor n^2.

A336124 a(n) = A122111(n) mod 4.

Original entry on oeis.org

1, 2, 0, 3, 0, 2, 0, 1, 1, 0, 0, 2, 0, 0, 2, 3, 0, 3, 0, 0, 0, 0, 0, 2, 3, 0, 1, 0, 0, 2, 0, 3, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 1, 1, 0, 0, 0, 3, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 1, 0, 0, 3, 0, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 3, 0, 3, 0, 0, 0, 0, 2
Offset: 1

Views

Author

Antti Karttunen, Jul 15 2020

Keywords

Crossrefs

Programs

  • PARI
    A064989(n) = {my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f)};
    A122111(n) = if(1==n,n,prime(bigomega(n))*A122111(A064989(n)));
    A336124(n) = (A122111(n)%4);

Formula

a(n) = A010873(A122111(n)).

A353526 The smallest prime not dividing n, reduced modulo 4.

Original entry on oeis.org

2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 1, 2, 3, 2, 3, 2, 1, 2, 3, 2
Offset: 1

Views

Author

Antti Karttunen, Apr 24 2022

Keywords

Crossrefs

Programs

  • Mathematica
    a[n_] := Module[{p = 2}, While[Divisible[n, p], p = NextPrime[p]]; Mod[p, 4]]; Array[a, 100] (* Amiram Eldar, Jul 25 2022 *)
  • PARI
    A053669(n) = forprime(p=2, , if(n%p, return(p))); \\ From A053669
    A353526(n) = (A053669(n)%4);

Formula

a(n) = A010873(A053669(n)).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{p prime} ((p mod 4)*(p-1)/(Product_{q prime, q <= p} q)) = 2.2324714414... . - Amiram Eldar, Jul 25 2022

A010883 Simple periodic sequence: repeat 1,2,3,4.

Original entry on oeis.org

1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1
Offset: 0

Views

Author

Keywords

Comments

Partial sums are given by A130482(n) + n + 1. - Hieronymus Fischer, Jun 08 2007
1234/9999 = 0.123412341234... - Eric Desbiaux, Nov 03 2008

Crossrefs

Cf. A177037 (decimal expansion of (9+2*sqrt(39))/15). - Klaus Brockhaus, May 01 2010

Programs

Formula

a(n) = 1 + (n mod 4). - Paolo P. Lava, Nov 21 2006
From Hieronymus Fischer, Jun 08 2007: (Start)
a(n) = A010873(n) + 1.
Also a(n) = (1/2)*(5 - (-1)^n - 2*(-1)^((2*n - 1 + (-1)^n)/4)).
G.f.: g(x) = (4*x^3 + 3*x^2 + 2*x + 1)/(1 - x^4) = (4*x^5 - 5*x^4 + 1)/((1 - x^4)*(1-x)^2). (End)
a(n) = 5/2 - cos(Pi*n/2) - sin(Pi*n/2) - (-1)^n/2. - R. J. Mathar, Oct 08 2011

A065882 Ultimate modulo 4: right-hand nonzero digit of n when written in base 4.

Original entry on oeis.org

1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 2, 1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 3, 1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 2, 3, 2, 1, 2, 3, 1, 1, 2, 3, 2, 1
Offset: 1

Views

Author

Henry Bottomley, Nov 26 2001

Keywords

Comments

From Bradley Klee, Sep 12 2015: (Start)
In some guise, this sequence is a linear encoding of the three fixed-point half-hex tilings (cf. Baake & Grimm, Frettlöh). Applying a permutation, morphism x -> 123x becomes x -> x123, which has three fixed points. Applying a partition, morphism x -> x123 becomes x ->{{3,2},{x,1}} or
3 2 3 2
3 1 2 1
3 2 3 2 3 2
x -> x 1 -> x 1 1 1 -> etc.,
which is the substitution rule for the half-hex tiling when the numbers 1,2,3 determine the direction of a dissecting diameter inscribed on each hexagon.
(End)

Examples

			a(7)=3 and a(112)=3, since 7 is written in base 4 as 13 and 112 as 1300.
		

References

  • M. Baake and U. Grimm, Aperiodic Order Vol. 1, Cambridge University Press, 2013, page 205.

Crossrefs

In base 2 this is A000012, base 3 A060236 and base 10 A065881.
Defining relations for g.f. similar to A014577.

Programs

  • Maple
    f:= proc(n)
    local x:=n;
       while x mod 4 = 0 do x:= x/4 od:
       x mod 4;
    end proc;
    map(f, [$1..100]); # Robert Israel, Jan 05 2016
  • Mathematica
    Nest[ Flatten[ # /. {1 -> {1, 2, 3, 1}, 2 -> {1, 2, 3, 2}, 3 -> {1, 2, 3, 3}}] &, {1}, 4] (* Robert G. Wilson v, May 07 2005 *)
    b[n_] := CoefficientList[Series[
        With[{f0 = (x + 2 x^2 + 3 x^3)/(1 - x^4)},
         Nest[ (# /. x -> x^4) + f0 &, f0, Ceiling[Log[4, n/3]]]],
    {x, 0, n}], x][[2 ;; -1]]; b[100](* Bradley Klee, Sep 12 2015 *)
    Table[Mod[n/4^IntegerExponent[n, 4], 4], {n, 1, 120}] (* Clark Kimberling, Oct 19 2016 *)
  • PARI
    a(n) = (n/4^valuation(n,4))%4; \\ Joerg Arndt, Sep 13 2015
    
  • Python
    def A065882(n): return (n>>((~n & n-1).bit_length()&-2))&3 # Chai Wah Wu, Aug 21 2023

Formula

If n mod 4 = 0 then a(n) = a(n/4), otherwise a(n) = n mod 4. a(n) = A065883(n) mod 4.
Fixed point of the morphism: 1 ->1231, 2 ->1232, 3 ->1233, starting from a(1) = 1. Sequence read mod 2 gives A035263. a(n) = A007913(n) mod 4. - Philippe Deléham, Mar 28 2004
G.f. g(x) satisfies g(x) = g(x^4) + (x + 2 x^2 + 3 x^3)/(1 - x^4). - Bradley Klee, Sep 12 2015

A163540 The absolute direction (0=east, 1=south, 2=west, 3=north) taken by the type I Hilbert's Hamiltonian walk A163357 at the step n.

Original entry on oeis.org

0, 1, 2, 1, 1, 0, 3, 0, 1, 0, 3, 3, 2, 3, 0, 0, 1, 0, 3, 0, 0, 1, 2, 1, 0, 1, 2, 2, 3, 2, 1, 1, 1, 0, 3, 0, 0, 1, 2, 1, 0, 1, 2, 2, 3, 2, 1, 2, 2, 3, 0, 3, 3, 2, 1, 2, 3, 2, 1, 1, 0, 1, 2, 1, 1, 0, 3, 0, 0, 1, 2, 1, 0, 1, 2, 2, 3, 2, 1, 1, 0, 1, 2, 1, 1, 0, 3, 0, 1, 0, 3, 3, 2, 3, 0, 0, 0, 1, 2, 1, 1, 0
Offset: 1

Views

Author

Antti Karttunen, Aug 01 2009

Keywords

Comments

Taking every sixteenth term gives the same sequence: (and similarly for all higher powers of 16 as well): a(n) = a(16*n).

Crossrefs

a(n) = A163540(A008598(n)) = A004442(A163541(n)). See also A163542.

Programs

  • Mathematica
    HC = {L[n_ /; IntegerQ[n/2]] :> {F[n], L[n], L[n + 1], R[n + 2]},
       R[n_ /; IntegerQ[(n + 1)/2]] :> {F[n], R[n], R[n + 3], L[n + 2]},
       R[n_ /; IntegerQ[n/2]] :> {L[n], R[n + 1], R[n], F[n + 3]},
       L[n_ /; IntegerQ[(n + 1)/2]] :> {R[n], L[n + 3], L[n], F[n + 1]},
       F[n_ /; IntegerQ[n/2]] :> {L[n], R[n + 1], R[n], L[n + 3]},
       F[n_ /; IntegerQ[(n + 1)/2]] :> {R[n], L[n + 3], L[n], R[n + 1]}};
    a[1] = F[0]; Map[(a[n_ /; IntegerQ[(n - #)/16]] :=
        Part[Flatten[a[(n + 16 - #)/16] /. HC /. HC], #]) &, Range[16]];
    Part[FoldList[Mod[Plus[#1, #2], 4] &, 0,
      a[#] & /@ Range[4^4] /. {F[n_] :> 0, L[n_] :> 1, R[n_] :> -1}],
    2 ;; -1] (* Bradley Klee, Aug 07 2015 *)
  • Scheme
    (define (A163540 n) (modulo (+ 3 (A163538 n) (A163539 n) (abs (A163539 n))) 4))

Formula

a(n) = A010873(A163538(n)+A163539(n)+abs(A163539(n))+3).

A353630 Arithmetic derivative of primorial base exp-function, reduced modulo 4.

Original entry on oeis.org

0, 1, 1, 1, 2, 1, 1, 3, 0, 3, 3, 3, 2, 1, 3, 1, 0, 1, 3, 3, 2, 3, 1, 3, 0, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 0, 3, 3, 3, 2, 3, 3, 1, 0, 1, 1, 1, 2, 3, 1, 3, 0, 3, 1, 1, 2, 1, 3, 1, 2, 1, 3, 1, 0, 1, 3, 3, 2, 3, 1, 3, 0, 1, 1, 1, 2, 1, 1, 3, 0, 3, 3, 3, 2, 1, 3, 1, 0, 1, 3, 1, 0, 1, 1, 1, 2, 3, 1, 3, 0, 3, 1, 1, 2, 1
Offset: 0

Views

Author

Antti Karttunen, May 01 2022

Keywords

Crossrefs

Cf. A010873, A166486 (parity of terms), A276086, A327860, A328572, A353493, A353640.
Cf. A353631, A353632 (bisections).
Cf. also A353486.

Programs

  • PARI
    A353630(n) = { my(s=0, m=1, p=2, e); while(n, e = (n%p); m *= (p^e); s += (e/p); n = n\p; p = nextprime(1+p)); ((s*m)%4); };

Formula

a(n) = A010873(A327860(n)).
a(n) = A353493(A276086(n)).
a(n) = A010873(A328572(n)*A353640(n)). [Note that all terms of A328572 are odd]
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