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.

Previous Showing 71-72 of 72 results.

A375489 Omit the trailing zeros from double factorial of even numbers (A000165).

Original entry on oeis.org

1, 2, 8, 48, 384, 384, 4608, 64512, 1032192, 18579456, 37158912, 817496064, 19619905536, 510117543936, 14283291230208, 42849873690624, 1371195958099968, 46620662575398912, 1678343852714360832, 63777066403145711616, 255108265612582846464, 10714547155728479551488
Offset: 0

Views

Author

Stefano Spezia, Aug 18 2024

Keywords

Crossrefs

Cf. A000165, A004154, A005843, A011557, A027868, A122840, A358987.

Programs

  • Mathematica
    a[n_]:=2^n*n!/10^IntegerExponent[n!,10]; Array[a,22,0]

Formula

a(n) = A000165(n)/10^A027868(n).
a(n) = a(n-1)*(2*n)/10^A122840(2*n) for n > 0.

A385978 Number of trailing zeros in (10*n)^(10*n).

Original entry on oeis.org

10, 20, 30, 40, 50, 60, 70, 80, 90, 200, 110, 120, 130, 140, 150, 160, 170, 180, 190, 400, 210, 220, 230, 240, 250, 260, 270, 280, 290, 600, 310, 320, 330, 340, 350, 360, 370, 380, 390, 800, 410, 420, 430, 440, 450, 460, 470, 480, 490, 1000, 510, 520, 530, 540
Offset: 1

Views

Author

Marco Ripà, Jul 13 2025

Keywords

Examples

			a(2) = 20 since 20^(10*2) = 104857600000000000000000000 has 20 trailing zeros.

Links

Crossrefs

Cf. A007814, A011557, A027868, A112765, A122840, A356946.

Programs

  • Mathematica
    a[n_] := 10 n (IntegerExponent[n, 10] + 1)  Table[a[n], {n, 1, 30}]
  • PARI
    a(n) = 10*n*(valuation(n,10)+1); \\ Michel Marcus, Jul 14 2025

Formula

a(n) = 10*n*(A122840(n) + 1).
Previous Showing 71-72 of 72 results.

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

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