# Questions tagged [oeis]

For questions related to the On-Line Encyclopedia of Integer Sequences.

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### Sequence $\{a_n\}$ where $a_n$ is the smallest proper multiple of $a_{n-1}$ containing $a_{n-2}$ in its digits

Recently, I've been interested in sequences $\{a_n\}$ where $a_n$ is the smallest proper multiple (multiple of a number larger than itself) of $a_{n-1}$ containing $a_{n-2}$ in its digits. A number $Y$...
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### Is it known whether or not OEIS sequence A091308 is finite?

OEIS sequence A038395 is defined as the concatenation of the first $n$ odd numbers in reverse order: $1,$ $31,$ $531,$ $7531,$ $97531,$ $1197531,$ etc., and A091308 is the sequence of primes in ...
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### Factorizations not sharing digits with original number

The sequence A371862 is "Positive integers that can be written as the product of two or more other integers, none of which uses any of the digits in the number itself." In the extended ...
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### Orientable necklaces and complements

I'm trying to understand the OEIS sequence A059078: Number of orientable necklaces with 2n beads and two colors which when turned over produce their own color complement. 0, 0, 0, 1, 2, 6, 12, 27, 54,...
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### What is the number of integers divisible by either 2, 3, or 5 from the integers 1 to $n+1$? [closed]

I am interested in integer sequence A254828 (https://oeis.org/A254828), but from the link it seems to have a recursive formula $a(n) = a(n-1) + a(n-30) - a(n-31)$. As joriki said, they are the number ...
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### Dodecahedral number visualization

The dodecahedral numbers, 0, 1, 20, 84, 220, 455, 816, 1330, 2024, 2925, 4060, ... numbers of the form ${3 n \choose 3}$ (A006566). Does anyone have a good visualization of these? In particular, I'd ...
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### Examples of palindromic polynomial sequences

In the OEIS you can find the coefficients of the h-polynomials for the associahedra, the Narayana polynomials A001263; for the stellahedra, A046802; and for the permutahedra, the Eulerian polynomials ...
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### Discrepancy in the number of simplices in the barycentric subdivision of an $n$-simplex

According to OEIS, the number of simplices in the barycentric subdivision of an $n$-simplex is either given by the sequence: (A002050): 1, 5, 25, 149, 1081, 9365, 94585, 1091669, 14174521, 204495125, ...
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### Squares in the hypercube and humps in Motzkin paths

The number of squares with vertices coming from the vertices of the $n$-dimensional hypercube $\{0,1\}^n$ is given by $$2^{n-3}\sum_{j=1}^{n} \binom{n}{j}\binom{n-j}{j}.$$ The $0$-indexed sequence ...
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### Brun's theorem - notation

The series $1,3,6,9,12,14$ represent the first six terms of the series A168045 on OEIS. The formula for this says $a_n = 2n + n / log n + O(n / (log n)^2)$. I do not understand this notation. What ...
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