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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A090162 Values of binomial(Fibonacci(2k)*Fibonacci(2k+1),Fibonacci(2k-1)*Fibonacci(2k)-1).

Original entry on oeis.org

1, 3003, 61218182743304701891431482520
Offset: 1

Views

Author

Eric W. Weisstein, Nov 23 2003 and Wolfdieter Lang, Dec 01 2003

Keywords

Comments

These numbers are known to occur at least six times in Pascal's triangle.
The next term is approximately 3.537 * 10^204 and is in the b-file.
The numbers of digits in a(n), n >= 1, are given in A100022.

Crossrefs

Subsequence of A003015.

Programs

  • Maple
    a := proc(n) local a,b,s,p; s:= 1+sqrt(5); p:=16^n;
    a := 4-2*p*s^(-4*n-1)+(s+2)*s^(4*n-1)/p:
    b := 1+p*((s-2)^(1-4*n)/2-s^(-1-4*n)*(2+s)):
    GAMMA(a/5)/(GAMMA(b/5)*GAMMA(1+(a-b)/5)) end:
    digits := [1, 4, 29, 205, 1412]: A := n -> round(evalf(a(n),digits[n]+10)):
    A(4); # Peter Luschny, Jul 15 2017
  • Mathematica
    Table[Binomial[Fibonacci[2k]Fibonacci[2k+1],Fibonacci[2k-1] Fibonacci[2k]-1], {k,4}] (* Harvey P. Dale, Aug 18 2011 *)
  • PARI
    A090162(n)=binomial(fibonacci(2*n+1)*fibonacci(2*n),fibonacci(2*n-1)*fibonacci(2*n)-1) \\ M. F. Hasler, Feb 17 2023
    
  • Python
    def A090162(n): return C(A000045(2*n+1)*A000045(2*n),A000045(2*n-1)*A000045(2*n)-1) # See A007318 for C(.,.). - M. F. Hasler, Feb 17 2023

Formula

a(n) = binomial(A089508(n), A081016(n-1)).
a(n) = binomial(A089508(n)+1, A081016(n-1)-1).
a(n) = Gamma(x)/(Gamma(y)*Gamma(1+x-y)) with x = A206351(n+1) and y = A081016(n-1). - Peter Luschny, Jul 15 2017

A137905 Numbers that appear as binomial coefficients exactly twice.

Original entry on oeis.org

3, 4, 5, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 37, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 57, 58, 59, 60, 61, 62, 63, 64, 65, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 79, 80, 81, 82, 83, 85, 86, 87, 88
Offset: 1

Views

Author

David Wasserman, Feb 21 2008

Keywords

Comments

Complement of A006987; a(n) = A058084(a(n)). - Reinhard Zumkeller, Mar 20 2009

Examples

			7 is a member because 7 = binomial(7, 1) = binomial(7, 6) and no other binomial coefficient equals 7. [clarified by _Jonathan Sondow_, Jan 12 2018]
		

Crossrefs

Programs

  • PARI
    isok(n) = (sum(i=0, n, sum(j=0, i, binomial(i,j)==n)) == 2) \\ Michel Marcus, Jun 16 2013

Formula

a(n) = A185024(n+1). - Elijah Beregovsky, May 14 2019
Showing 1-2 of 2 results.