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- The On-Line Encyclopedia of Integer Sequences (OEIS)
Last modified December 5 17:04 EST 2025 Contains 390834 sequences
- Welcome - OeisWiki - The On-Line Encyclopedia of Integer Sequences (OEIS)
NJAS set up a non-profit foundation, The OEIS Foundation Inc , whose purpose is to own, maintain and raise funds to support The On-Line Encyclopedia of Integer Sequences® (OEIS®)
- OeisWiki - The On-Line Encyclopedia of Integer Sequences (OEIS)
Important: The main OEIS lookup page is https: oeis org Use that page for looking up a sequence, searching the database, contributing new sequences, editing sequences, etc
- A000001 - OEIS
He gives n = 36355 as an example It would be nice to have enough values of n to create an OEIS entry for them - N J A Sloane, Jan 02 2021 I conjecture that a (i) * a (j) <= a (i*j) for all nonnegative integers i and j - Jorge R F F Lopes, Apr 21 2024
- Hints for Using - The On-Line Encyclopedia of Integer Sequences (OEIS)
If your sequence isn't in the database - and is of general interest - please send it to the OEIS This will help other people who come across the same sequence (and will preserve your name for posterity)
- A000108 - OEIS
This is probably the longest entry in the OEIS, and rightly so The solution to Schröder's first problem: number of ways to insert n pairs of parentheses in a word of n+1 letters E g , for n=2 there are 2 ways: ( (ab)c) or (a (bc)); for n=3 there are 5 ways: ( (ab) (cd)), ( ( (ab)c)d), ( (a (bc))d), (a ( (bc)d)), (a (b (cd)))
- A000040 - OEIS
A number n is prime if and only if it is different from zero and different from a unit and each multiple of n decomposes into factors such that n divides at least one of the factors This applies equally to the integers (where a prime has exactly four divisors (the definition of divisors is relaxed such that they can be negative)) and the positive integers (where a prime has exactly two
- A002487 - OEIS
a # Yosu Yurramendi, Oct 04 2014 (Scheme) ;; An implementation of memoization-macro definec can be found for example in: https: oeis org wiki Memoization
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