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 21-23 of 23 results.

A331231 Numbers k such that the number of factorizations of k into distinct factors > 1 is even.

Original entry on oeis.org

6, 8, 10, 14, 15, 16, 21, 22, 26, 27, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 96, 106, 111, 115, 118, 119, 120, 122, 123, 125, 129, 133, 134, 141, 142, 143, 144, 145, 146, 155, 158, 159, 160, 161, 166
Offset: 1

Views

Author

Gus Wiseman, Jan 12 2020

Keywords

Comments

First differs from A319238 in having 300.

Crossrefs

The version for integer partitions is A001560.
The version for strict integer partitions is A090864.
The version for set partitions appears to be A016789.
The non-strict version is A331051.
The version for primes (instead of evens) is A331201.
The odd version is A331230.
Factorizations are A001055 with image A045782 and complement A330976.
Strict factorizations are A045778 with image A045779 and complement A330975.
The least number with n strict factorizations is A330974(n).
Cf. A001318, A045780, A045783, A318286, A328966, A330973, A330991, A330997, A331022, A331023/A331024, A331050, A331200, A331232.

Programs

  • Mathematica
    strfacs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[strfacs[n/d],Min@@#>d&]],{d,Rest[Divisors[n]]}]];
Select[Range[100],EvenQ[Length[strfacs[#]]]&]

A328970 Numbers k such that the coefficient of x^k in the expansion of Product_{j>=1} (1 - x^j) / (1 - x^prime(j)) is zero.

Original entry on oeis.org

2, 3, 9, 11, 12, 14, 17, 18, 19, 20, 28, 44, 47, 51, 52, 55, 56, 58, 59, 62, 64, 65, 69, 80, 81, 82, 83, 87, 91, 92, 94, 96, 99, 105, 106, 107, 113, 118, 119, 126, 127, 131, 147, 155, 157, 160, 161, 162, 164, 178, 179, 180, 215, 218, 224, 227, 257, 259, 269, 295
Offset: 1

Views

Author

Ilya Gutkovskiy, Nov 01 2019

Keywords

Comments

Numbers k such that number of partitions of k into an even number of distinct nonprime parts equals number of partitions of k into an odd number of distinct nonprime parts.
Positions of 0's in A302234.

Crossrefs

Cf. A002095, A018252, A090864, A096258, A302234.

Programs

  • Mathematica
    a[j_] := a[j] = If[j == 0, 1, -Sum[Sum[Boole[!PrimeQ[d]] d, {d, Divisors[k]}] a[j - k], {k, 1, j}]/j]; Select[Range[300], a[#] == 0 &]
Flatten[Position[nmax = 300; Rest[CoefficientList[Series[Product[(1 - x^j)/(1 - x^Prime[j]), {j, 1, nmax}], {x, 0, nmax}], x]], 0]]

A329003 Numbers k such that the coefficient of x^k in the expansion of Product_{j>=2} (1 - x^Fibonacci(j)) is zero.

Original entry on oeis.org

3, 5, 6, 9, 10, 15, 16, 17, 21, 25, 26, 27, 28, 32, 34, 35, 37, 41, 42, 43, 44, 45, 46, 50, 52, 53, 56, 57, 60, 61, 63, 67, 68, 69, 70, 71, 72, 73, 74, 75, 79, 81, 82, 85, 86, 91, 92, 93, 98, 99, 102, 103, 105, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120
Offset: 1

Views

Author

Ilya Gutkovskiy, Nov 01 2019

Keywords

Comments

Numbers k such that number of partitions of k into an even number of distinct Fibonacci parts equals number of partitions of k into an odd number of distinct Fibonacci parts (1 counted as single Fibonacci number).
Positions of 0's in A093996.
Complement of A151661.

Crossrefs

Cf. A000045, A000119, A003107, A090864, A093996, A151661.

Programs

  • Mathematica
    Flatten[Position[Rest[CoefficientList[Series[Product[(1 - x^Fibonacci[j]), {j, 2, 21}], {x, 0, 130}], x]], 0]]
Previous Showing 21-23 of 23 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.