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.

A358990 a(n) is the product of the first n odd numbers not divisible by 5.

Original entry on oeis.org

1, 1, 3, 21, 189, 2079, 27027, 459459, 8729721, 183324141, 4216455243, 113844291561, 3301484455269, 102346018113339, 3377418597740187, 124964488116386919, 4873615036539089841, 199818216498102683481, 8592183309418415389683, 403832615542665523315101, 19787798161590610642439949
Offset: 0

Views

Author

Stefano Spezia, Dec 09 2022

Keywords

Comments

Unlike the factorial number n!, but like A356858(n), a(n) does not have trailing zeros.

Crossrefs

Cf. A000142, A045572, A356858.
Cf. A358991 (number of zero digits), A358992 (number of digits), A358993 (number of nonzero digits).

Programs

  • Mathematica
    Table[Product[2*k+2*Floor[(k-3)/4]+1,{k,n}],{n,0,20}]
  • PARI
    f(n) = 2*n - 1 + (n+1)\4 * 2; \\ A045572
a(n) = prod(k=1, n, f(k)); \\ Michel Marcus, Dec 10 2022

Formula

a(n) = Product_{k=1..n} A045572(k).

A358991 a(n) is the number of zero digits in the product of the first n odd numbers not divisible by 5.

Original entry on oeis.org

0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 2, 1, 0, 2, 1, 1, 2, 2, 3, 2, 2, 2, 3, 2, 4, 5, 2, 4, 1, 3, 4, 5, 6, 9, 5, 4, 6, 4, 7, 7, 10, 5, 7, 10, 8, 9, 8, 4, 7, 4, 15, 9, 4, 7, 12, 9, 8, 14, 12, 5, 14, 12, 6, 11, 10, 14, 17, 17, 11, 19, 11, 15, 19, 15, 13, 14, 11, 19
Offset: 0

Views

Author

Stefano Spezia, Dec 09 2022

Keywords

Crossrefs

Cf. A045572, A055641, A356859, A358990.
Cf. A358992 (number of digits), A358993 (number of nonzero digits).

Programs

  • Mathematica
    Table[Count[IntegerDigits[Product[2i+2Floor[(i-3)/4]+1, {i, n}]], 0], {n, 0, 80}]

Formula

a(n) = A055641(A356990(n)).

A358992 a(n) is the number of digits in the product of the first n odd numbers not divisible by 5.

Original entry on oeis.org

1, 1, 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 15, 16, 18, 19, 21, 22, 24, 26, 28, 29, 31, 33, 35, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 82, 84, 86, 88, 90, 92, 94, 96, 99, 101, 103, 105, 107, 109, 112, 114, 116
Offset: 0

Views

Author

Stefano Spezia, Dec 09 2022

Keywords

Crossrefs

Cf. A045572, A055642, A356860, A358990.
Cf. A358991 (number of zero digits), A358993 (number of nonzero digits).

Programs

  • Mathematica
    Table[Length[IntegerDigits[Product[2i+2Floor[(i-3)/4]+1, {i, n}]]], {n, 0, 65}]

Formula

a(n) = A055642(A358990(n)).
Showing 1-3 of 3 results.

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

Content is available under The OEIS End-User License Agreement.