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.

A113765 Define the first two terms to be 1 and 7. All the other terms are obtained by concatenating the two previous terms.

Original entry on oeis.org

1, 7, 17, 717, 17717, 71717717, 1771771717717, 717177171771771717717, 1771771717717717177171771771717717, 7171771717717717177171771771717717717177171771771717717
Offset: 0

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Author

Parthasarathy Nambi, Jan 18 2006

Keywords

Comments

a(n) has Fibonacci(n) digits and the sum of all digits is given by Fibonacci(n-2)+7*Fibonacci(n-1) for all n>4. - Stefan Steinerberger, Jan 21 2006

Examples

			The third term is 17 and it is obtained by concatenating the two previous terms 1 and 7.

Crossrefs

Cf. A008352, A113526.
Cf. A000045 - the Fibonacci numbers.

Extensions

More terms from Stefan Steinerberger, Jan 21 2006

A334025 a(0)=0, a(1)=1; and a(n) = {2*a(n-2), 2*a(n-1)}, where {x,y} is the concatenation of x and y.

Original entry on oeis.org

0, 1, 2, 24, 448, 48896, 89697792, 97792179395584, 179395584195584358791168, 195584358791168358791168391168717582336, 358791168391168717582336391168717582336717582336782337435164672
Offset: 0

Views

Author

Jamie Robert Creasey, Apr 14 2020

Keywords

Comments

This sequence, due to the process of concatenating one number with another, bears similarities to A131293 and other familiar sequences. However, unlike A131293, this sequence increases at a faster rate. It happens due to the multiplier applied to the existing terms, which increases the number of digits present in the successive term drastically (see a(7) and a(8)). a(11) is too large to include here and has 102 digits.

Examples

			a(2) = {2*a(2-2), 2*a(2-1)} = {2*0, 2*1} = 02 = 2.
a(5) = {2*a(5-2), 2*a(5-1)} = {2*24, 2*448} = 48896.

Crossrefs

Cf. A002605, A061107, A108047, A131293, A008352, A113526, A104458.

Programs

  • Mathematica
    a[0] = 0; a[1] = 1; a[n_] := a[n] = FromDigits @ Join[IntegerDigits[2*a[n - 2]], IntegerDigits[2*a[n - 1]]]; Array[a, 11, 0] (* Amiram Eldar, Apr 18 2020 *)
Showing 1-2 of 2 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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