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 1-3 of 3 results.

A050923 a(n) = 2^(n!).

Original entry on oeis.org

2, 2, 4, 64, 16777216, 1329227995784915872903807060280344576
Offset: 0

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Author

Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 30 1999

Keywords

Comments

For n > 0, every n-fold repetition of a(n) is a "powerful" arithmetic progression with difference 0; e.g., for n = 4 we get a(4) = 16777216 and in the generated repeating sequence of length 4 the k-th term is a k-th power (1 <= k <= n): 16777216 = 16777216^1, 16777216 = 4096^2, 16777216 = 256^3, 16777216 = 64^4. - Martin Renner, Aug 16 2017
From Jianing Song, Jul 20 2021: (Start)
Let F_q be the finite field with q elements, then in F_a(n), every polynomial of degree at most n splits into linear factors.
Union_{n>=0} F_a(n) is the algebraic clousre of F_2, which is the unique algebraically closed field with characteristic 2 and transcendence degree 0 (note that an algebraically closed field is uniquely determined by its characteristic and transcendence degree). Union_{n>=0} F_(2^lcm(1,2,...,n)) = Union_{n>=0} F_A178981(n) gives the same field.
Obviously, here 2 can be replaced by any prime p provided that {a(n)} is defined as a(n) = p^(n!). (End)
For n >= 1, the number of digits of a(n) is A317873(n). - Martin Renner, Mar 24 2024

Crossrefs

Programs

Formula

a(n) = a(n-1)^n, a(0)=2.
a(n) = A000079(A000142(n)).
Sum_{n>=1} 1/a(n) = A092874. - Amiram Eldar, Oct 27 2020

A145572 Numerators of partial sums for Liouville's constant, read as base 2 (binary) numbers.

Original entry on oeis.org

1, 3, 49, 12845057, 1017690263500988729456314874071089153, 4222921592695952872362526736376161058920018764920519780147745963811744865992371113095993596088044297100172572224585271942341064532181870606866447799704872724575357044373908131956500952542608981420222196042850818326529
Offset: 1

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Author

Wolfdieter Lang Mar 06 2009

Keywords

Comments

a(n) is A145571(n) (a decimal number with digits only from {0,1}) read as base 2 number converted back into decimal notation.
The sequence of digit lengths is 1,1,2,8,37,217,1518,... (see A317873).
This sequence gives the numerators of the partial sums for the constant A092874 (called there "binary" Liouville number). See the B(n) formula below. - Wolfdieter Lang, Apr 10 2024

Examples

			a(3)=49, because A145571(3)=110001, and the binary number 110001 translates to 2^5+2^4+2^0=32+16+1 = 49.
		

Crossrefs

Cf. A001563, A092874, A145571 (numerators of approximations for Liouville's number).
Cf. A317873.

Programs

  • Mathematica
    a[n_] := FromDigits[RealDigits[Sum[1/10^k!, {k, n}], 10, n!][[1]], 2]; Array[a, 6] (* Robert G. Wilson v, Aug 08 2018 *)
    Block[{k = 0}, NestList[#*2^(++k*k!) + 1 &, 1, 5]] (* Paolo Xausa, Jun 27 2024 *)

Formula

a(n) = A145571(n) interpreted as number in binary notation, then converted to decimal notation.
From Wolfdieter Lang, Apr 10 2024: (Start)
a(n) = Sum_{j=0..n} 2^(n! - j!) = 2^(n!)*B(n) = numerator(B(n)), where B(n) := Sum_{j=1..n} 1/2^(j!), for n >= 1 (Proof from the positions of 1 in A145571).
a(1) = 1, and a(n) = a(n-1)*2^z(n) + 1, where z(n) = n! - (n-1)! = A001563(n-1), for n >= 2.
(End)

A385949 Number of digits in 7^(n!).

Original entry on oeis.org

1, 1, 2, 6, 21, 102, 609, 4260, 34075, 306670, 3066692, 33733610, 404803314, 5262443074, 73674203025, 1105113045374, 17681808725979, 300590748341642, 5410633470149548, 102802035932841396, 2056040718656827910, 43176855091793386107, 949890812019454494354
Offset: 0

Views

Author

Vincenzo Librandi, Jul 24 2025

Keywords

Crossrefs

Programs

  • Mathematica
    Array[ Floor[#! Log10@7 + 1] &, 22]

Formula

a(n) = A055642(A220079(n)).
Showing 1-3 of 3 results.