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added 22 characters in body

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edited Feb 4, 2020 at 23:23

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Jelly, 1515 9 bytes

-,3,3,1ṫḢạ’×12Ɗ’3cạ×12$Ʋ

Try it online!Try it online!

A monadic link taking \$n\$ as its argument and returning \$a(n)\$.

Based on @LevelRiverSt’s clever Ruby answer so be sure to upvote that one too!

Thanks to @Grimmy for saving 6 bytes!

Explanation

-,3,3,1ṫ ’       | Sublist ofSubtract -1,3,3,1 starting at 
 the nth character (empty if n>4)
   Ʋ | Following as a Ḣmonad
3c       | Head (zero if- emptyNumber list)
of ways of picking (n-1) items from 3
  ạ   $ Ɗ | - Absolute difference from:
     ×12   |  ’×12 - |Multiply (n-1) × 12

Jelly, 15 bytes

-,3,3,1ṫḢạ’×12Ɗ

Try it online!

A monadic link taking \$n\$ as its argument and returning \$a(n)\$.

Based on @LevelRiverSt’s clever Ruby answer so be sure to upvote that one too!

Explanation

-,3,3,1ṫ        | Sublist of -1,3,3,1 starting at the nth character (empty if n>4)
        Ḣ       | Head (zero if empty list)
         ạ    Ɗ | Absolute difference from:
          ’×12  | (n-1) × 12

Jelly, 15 9 bytes

’3cạ×12$Ʋ

Try it online!

A monadic link taking \$n\$ as its argument and returning \$a(n)\$.

Based on @LevelRiverSt’s clever Ruby answer so be sure to upvote that one too!

Thanks to @Grimmy for saving 6 bytes!

Explanation

 ’       | Subtract 1 
       Ʋ | Following as a monad
3c       | - Number of ways of picking (n-1) items from 3
  ạ   $  | - Absolute difference from:
   ×12   |   - Multiply (n-1) × 12

Source Link

created Feb 4, 2020 at 23:07

Nick Kennedy

21.2k
3
17
43

Jelly, 15 bytes

-,3,3,1ṫḢạ’×12Ɗ

Try it online!

A monadic link taking \$n\$ as its argument and returning \$a(n)\$.

Based on @LevelRiverSt’s clever Ruby answer so be sure to upvote that one too!

Explanation

-,3,3,1ṫ        | Sublist of -1,3,3,1 starting at the nth character (empty if n>4)
        Ḣ       | Head (zero if empty list)
         ạ    Ɗ | Absolute difference from:
          ’×12  | (n-1) × 12