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 1-2 of 2 results.

A123703 a(1)=a(2)=1. For n >= 3, a(n) = |(product{k=1 to n-1} a(k)) - (sum{j=1 to n-1} a(j))|.

Original entry on oeis.org

1, 1, 1, 2, 3, 2, 2, 12, 264, 75744, 5758891776, 33165272341980979200, 1099935289708766240667530888404210286592, 1209857641546707521062997518664689369471121315619387834957574646785625397657600
Offset: 1

Views

Author

Leroy Quet, Oct 08 2006

Keywords

Crossrefs

Cf. A123702.

Programs

  • Mathematica
    f[l_List] := Append[l, Abs[Times @@ l - Plus @@ l]];Nest[f, {1, 1}, 12] (* Ray Chandler, Oct 09 2006 *)

Extensions

Extended by Ray Chandler, Oct 09 2006

A309080 Product minus sum of all previous terms in the sequence, starting with a(1) = 2 and a(2) = 5.

Original entry on oeis.org

2, 5, 3, 20, 570, 341400, 116758458000, 13632577445813641200000, 185847167817698504752014113195034069600000000, 34539169785859790805229099212216829464451540660176789302662465332580254227520000000000000
Offset: 1

Views

Author

Keywords

Examples

			a(4) = a(1)*a(2)*a(3) - (a(1) + a(2) + a(3)) = 2*5*3 - (2 + 5 + 3) = 20.
		

Crossrefs

Cf. A123702.

Programs

  • Mathematica
    x1 = 2; x2 = 5; p = x1 * x2; s = x1 + x2; x = p - s; A309080 = {x1, x2, x}; Do[p = p * x; s = s + x; x = p - s; AppendTo[A309080, x], {n, 16}]
  • Python
    a, n, p, s = [2,5], 2, 2, 2
    while n < 10:
        p, s, n = p*a[len(a)-1], s+a[len(a)-1], n+1
        a = a+[p-s]
    for n in range(1, 11): print(a[n-1], end=', ') # A.H.M. Smeets, Aug 22 2019

Formula

a(n) = Product_{k=1..n-1} a(k) - Sum_{k=1..n-1} a(k) with a(1) = 2, a(2) = 5.
Showing 1-2 of 2 results.