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calendar
2021

cover/jan/feb/mar/apr/may/jun/jul/aug/sep/oct/nov/dec

Cover A271999
Halogen sequence (the atomic numbers of the elements in group 17 in the periodic table).
1, 11, 17, 35, 53, 85, 117, ...
a(21) = 2021
January A248431
Number of length n+2 0..6 arrays with every three consecutive terms having the sum of some two elements equal to twice the third.
61, 105, 185, 327, 601, 1105, ...
a(7) = 2021
February A325250
Number of integer partitions of n whose omega-sequence is strict (no repeated parts). The omega-sequence of an integer partition is the sequence of lengths of the multisets obtained by repeatedly taking the multiset of multiplicities until a singleton is reached.
1, 1, 2, 2, 3, 2, 5, 2, 5, 4, ...
a(43) = 2021
March A238220
The total number of 5's in all partitions of n into an even number of distinct parts.
0, 0, 0, 0, 0, 0, 1, 1, 1, 1, ...
a(60) = 2021
a(36) = 120 depicted
April A266543
Number of n X 4 binary arrays with rows and columns lexicographically nondecreasing and row and column sums nonincreasing.
2, 4, 6, 12, 16, 27, 36, 57, ...
a(21) = 2021
May A025149
Number of partitions of n into distinct parts >= 4.
1, 0, 0, 0, 1, 1, 1, 1, 1, 2, ...
a(61) = 2021
a(36) = 120 depicted
June A005816
Number of 4-valent labeled graphs with n nodes where multiple edges and loops are allowed. Each node has 4 ends of edges and the order of the nodes is significant.
1, 1, 3, 15, 138, 2021, ...
a(5) = 2021
a(4) = 138 depicted
July A150600
Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 1), (-1, 0, 0), (0, 1, 1), (1, 0, -1), (1, 0, 1)}. None of the X,Y,Z coordinates can go negative.
1, 2, 7, 27, 109, 462, 2021, ...
a(6) = 2021
August A283528
The number of phi-partitions of n. The number of partitions n = a1 + a2 + ... + ak which have at least two parts and obey phi(n) = phi(a1) + phi(a2) + ... + phi(ak). phi is Euler's totient, the number of positive integers up to a given integer that are relatively prime to it.
0, 0, 1, 1, 2, 0, 3, 4, 8, 2, ...
a(49) = 2021
September A309692
Sum of the odd parts appearing among the largest parts of the partitions of n into 3 parts.
0, 0, 0, 1, 0, 3, 3, 11, 8, ...
a(44) = 2021
October A322439
Number of ordered pairs of integer partitions of n where no part of the first is greater than any part of the second.
1, 1, 3, 5, 11, 15, 33, 42, ...
a(16) = 2021
November A326540
Sum of all the parts in the partitions of n into 9 primes.
0, ..., 0, 18, 19, 20, 42, ...
a(43) = 2021
December A260744
Number of prime juggling patterns of period n using 2 balls. A prime juggling pattern repeats without visiting the same state more than once.
1, 2, 5, 10, 23, 48, 105, ...
a(11) = 2021

Each of the 13 designs (12 months plus cover) is based on a sequence from the Online Encyclopedia of Integer Sequences® in which the number 2021 occurs. OEIS is a registered trademark of the OEIS Foundation, Inc. This project is neither endorsed by nor affiliated with the OEIS.

Source Code

The source code will be made available some time in 2021, implemented in Haskell and C without any special libraries:

git clone https://code.mathr.co.uk/oeis-diagrams.git

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