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.

Showing 1-6 of 6 results.

A238754 Triangle read by rows: T(n,k) = A059383(n)/(A059383(k)*A059383(n-k)).

Original entry on oeis.org

1, 1, 1, 1, 15, 1, 1, 80, 80, 1, 1, 240, 1280, 240, 1, 1, 624, 9984, 9984, 624, 1, 1, 1200, 49920, 149760, 49920, 1200, 1, 1, 2400, 192000, 1497600, 1497600, 192000, 2400, 1, 1, 3840, 614400, 9216000, 23961600, 9216000, 614400, 3840, 1, 1, 6480, 1658880
Offset: 0

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Author

Tom Edgar, Mar 04 2014

Keywords

Comments

We assume that A059383(0)=1 since it would be the empty product.
These are the generalized binomial coefficients associated with the Jordan totient function J_4 given in A059377.
Another name might be the 4-totienomial coefficients.

Examples

			The first five terms in the fourth Jordan totient function are 1,15,80,240,624 and so T(4,2) = 240*80*15*1/((15*1)*(15*1))=1280 and T(5,3) = 624*240*80*15*1/((80*15*1)*(15*1))=9984.
The triangle begins
1
1 1
1 15  1
1 80  80   1
1 240 1280 240  1
1 624 9984 9984 624 1
		

Crossrefs

Programs

  • Sage
    q=100 #change q for more rows
    P=[0]+[i^4*prod([1-1/p^4 for p in prime_divisors(i)]) for i in [1..q]]
    [[prod(P[1:n+1])/(prod(P[1:k+1])*prod(P[1:(n-k)+1])) for k in [0..n]] for n in [0..len(P)-1]] #generates the triangle up to q rows.

Formula

T(n,k) = A059383(n)/(A059383(k)* A059383(n-k)).
T(n,k) = prod_{i=1..n} A059377(i)/(prod_{i=1..k} A059377(i)*prod_{i=1..n-k} A059377(i)).
T(n,k) = A059377(n)/n*(k/A059377(k)*T(n-1,k-1)+(n-k)/A059377(n-k)*T(n-1,k)).

A001088 Product of totient function: a(n) = Product_{k=1..n} phi(k) (cf. A000010).

Original entry on oeis.org

1, 1, 1, 2, 4, 16, 32, 192, 768, 4608, 18432, 184320, 737280, 8847360, 53084160, 424673280, 3397386240, 54358179840, 326149079040, 5870683422720, 46965467381760, 563585608581120, 5635856085811200, 123988833887846400, 991910671102771200, 19838213422055424000
Offset: 0

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Author

Keywords

Comments

a(n) is also the determinant of the symmetric n X n matrix M defined by M(i,j) = gcd(i,j) for 1 <= i,j <= n [Smith and Mansion]. - Avi Peretz (njk(AT)netvision.net.il), Mar 20 2001
The matrix M(i,j) = gcd(i,j) is sequence A003989. - Michael Somos, Jun 25 2012

Examples

			a(2) = 1 because the matrix M is: [1,1; 1,2] and det(A) = 1.
		

References

  • D. E. Knuth, The Art of Computer Programming. Addison-Wesley, Reading, MA, Vol. 2, p. 598.
  • M. Petkovsek et al., A=B, Peters, 1996, p. 21.

Crossrefs

Programs

Formula

a(n) = phi(1) * phi(2) * ... * phi(n).
Limit_{n->infinity} a(n)^(1/n) / n = exp(-1) * A124175 = 0.205963050288186353879675428232497466485878059342058515016427881513657493... (see Mathoverflow link). - Vaclav Kotesovec, Jun 09 2021

Extensions

a(0)=1 prepended by Alois P. Heinz, Jul 19 2023

A175836 a(n) = Product_{i=1..n} psi(i) where psi is the Dedekind psi function (A001615).

Original entry on oeis.org

1, 3, 12, 72, 432, 5184, 41472, 497664, 5971968, 107495424, 1289945088, 30958682112, 433421549568, 10402117189632, 249650812551168, 5991619501228032, 107849151022104576, 3882569436795764736
Offset: 1

Views

Author

Enrique Pérez Herrero, Sep 18 2010

Keywords

Comments

a(n) is also the determinant of the symmetric n X n matrix M defined by M(i,j) = A060648(gcd(i,j)) for 1 <= i,j <= n, note that A060648 is the Inverse Möbius transform of A001615. - Enrique Pérez Herrero, Aug 12 2011

Crossrefs

Programs

  • Haskell
    a175836 n = a175836_list !! (n-1)
    a175836_list = scanl1 (*) a001615_list
    -- Reinhard Zumkeller, Mar 01 2014
  • Maple
    A175836 := proc(n) option remember; local p; `if`(n<2,1, n*mul(1+1/p,p=factorset(n))*A175836(n-1)) end: # Peter Luschny, Feb 28 2014
  • Mathematica
    JordanTotient[n_,k_:1]:=DivisorSum[n,#^k*MoebiusMu[n/# ]&]/;(n>0)&&IntegerQ[n];
    DedekindPsi[n_]:=JordanTotient[n,2]/EulerPhi[n];
    A175836[n_]:=Times@@DedekindPsi/@Range[n]
  • PARI
    a=direuler(p=2, 100, (1+X)/(1-p*X));for(i=2,#a,a[i]*=a[i-1]);a
    \\ Charles R Greathouse IV, Jul 29 2011
    

Formula

a(n) = A059381(n)/A001088(n).

A059382 Product J_3(i), i=1..n.

Original entry on oeis.org

1, 7, 182, 10192, 1263808, 230013056, 78664465152, 35241680388096, 24739659632443392, 21474024560960864256, 28560452666077949460480, 41584019081809494414458880, 91318505903653649734151700480, 218616503133346837463559170949120
Offset: 1

Views

Author

N. J. A. Sloane, Jan 28 2001

Keywords

Comments

a(n) is also the determinant of the symmetric n X n matrix M defined by M(i,j) = gcd(i,j)^3 for 1 <= i,j <= n. - Avi Peretz (njk(AT)netvision.net.il), Mar 22 2001

References

  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 203, #17.

Crossrefs

Programs

  • Mathematica
    JordanTotient[n_, k_:1]:=DivisorSum[n, #^k*MoebiusMu[n/#]&]/; (n>0)&&IntegerQ[n]; A059382[n_]:=Times@@(JordanTotient[#, 3]&/@Range[n]); (* Enrique Pérez Herrero, Aug 06 2011 *)

A059384 a(n) = Product_{i=1..n} J_5(i).

Original entry on oeis.org

1, 31, 7502, 7441984, 23248758016, 174412182636032, 2931171141381153792, 93047096712003345973248, 5471727569246068763302821888, 529903984716066283313298482921472, 85341036738522474927606720674503065600, 20487310643596659421020979792003903940198400
Offset: 1

Views

Author

N. J. A. Sloane, Jan 28 2001

Keywords

Comments

a(n) is also the determinant of the symmetric n X n matrix M defined by M(i,j) = gcd(i,j)^5 for 1 <= i,j <= n. - Avi Peretz (njk(AT)netvision.net.il), Mar 22 2001

References

  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 203, #17.

Crossrefs

Programs

  • Mathematica
    JordanTotient[n_Integer, k_: 1] := DivisorSum[n, #^k*MoebiusMu[n/#] &];  f[n_] := Times @@ (JordanTotient[#, 5] & /@ Range[n]); (* Enrique Pérez Herrero *)  Array[f, 11] (* Robert G. Wilson v, Oct 08 2011 *)

A239672 Product_{i=1..n} J_6(i) where J_6(i) = A069091(i).

Original entry on oeis.org

1, 63, 45864, 184923648, 2889247076352, 132512427909808128, 15589822118733106642944, 4022922418094840702998413312, 2135013202351949099169693925638144, 2101519115233451721701919767332732796928, 3722967203782973732098252983015976113725767680
Offset: 1

Views

Author

Tom Edgar, Mar 23 2014

Keywords

Comments

This is the generalized factorial for A069091.
a(n) is also the determinant of the symmetric n X n matrix M defined by M(i,j) = gcd(i,j)^6 for 1 <= i,j <= n.

References

  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 203, #17.

Crossrefs

Programs

  • Sage
    q=15 # change q for more terms
    J6=[i^6*prod([1-1/p^6 for p in prime_divisors(i)]) for i in [1..q]]
    [prod(J6[0:i+1]) for i in [0..q-1]]
Showing 1-6 of 6 results.