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Jelly, 3 bytes Rç/ Try it online! Takes f as the helper link. Very basic, R casts to range, then ç/ reduces by the helper link
JavaScript, 20 bytes Outputs false for truthy and true for falsey. a=>a.some(x=>x-a[0]) Try it online! Outputs true and false as normal. a=>new Set(a).size<2 Try it online!
JavaScript (Node.js), 87 bytes f=(a,b=2,c=a-b,d=(a,b=2)=>b<a?a%b&&d(a,b+1):1,e=a=>d(++a)?a:e(a))=>d(c)?[b,c]:f(a,e(b)) Try it online!
Husk, 9 bytes ḟo=⁰Σπ2İp Try it online! Explanation ḟo=⁰Σπ2İp İp take the infinite list of primes π2 cartesian power 2 (all possible pairs) ḟo first pair which satisfie...
JavaScript, 227 bytes (n,k,A,C=(a,b)=>a?[...C(--a,b),b(a)]:[],f=m=>m?C(n+1,i=>f(m-1).map(([p,s])=> [[...p,i],s+i])).flat():[[[],0]])=>f(k).map(([b,s])=>a=s-n?a:b.map((a,b)=>...
Python 3, 39 bytes f=lambda x:x if x<2else 2*f(x-1)+f(x-2) Generic recursive implementation Try it online!
APL (Dyalog Classic), 20 18 17 16 bytes ⊢/,+.×⍣⎕⍨∘.+⍨⌽⍳2 Matrix implementation, requires ⎕IO←0. Thanks to @Razetime for the idea, -3 bytes by me Try it online! APL (Dyalog Classic), 19 18 byt...
Stax, 5 bytes òP^↓Φ Run and debug it Same idea as Quintec's answer. Input as a floating point number. Explanation 1gpun+ 1 start with 1 gp apply the following till a fixpoint...
PowerShell, 15 bytes "Hello, World!" Try it online!
Jelly, 7 bytes =þ`ÄŒDḢ Try it online!
Scala 3, 50 44 bytes ? => ?.indices zip?map(?take _+1 count _.==) Try it in Scastie! This is an annoying, stupid approach. The more elegant one using inits was much longer (x=>x.inits.to...
Husk, 4 bytes Sz#ḣ Try it online! Explanation Sz#ḣ Sz zip the input ḣ with its prefixes # using the count function
APL(Dyalog Unicode), 34 29 bytes SBCS Saved 5 bytes thanks to Razetime! {2>s←⌈2÷⍨≢⍵:⍵⋄,⍉↑∇¨s(↑,⍥⊂↓)⍵} Try it on APLgolf! {2>s←⌈2÷⍨≢⍵:⍵⋄,⍉↑∇¨s(↑,⍥⊂↓)⍵} { } ...
BQN, 14 bytesSBCS ∾⟜•FMT"∾⟜•FMT" Run online! Assumes •FMT will format a string by placing it in quotes, which depends on the BQN system in use. After (⟜) applies its right operand •FMT to the ...
Scala 3, 68 bytes _.zipWithIndex.flatMap(_.zipWithIndex.filter(_._1)map(_._2)map _.->) Try it in Scastie! Takes a List[List[Boolean]], returns a List[(Int, Int)]. This abuses underscores a ...
BQN, 44 bytesSBCS +´{(≠↑𝕨-𝔽)⊸+2↓⊑∨(≍×𝕨≥⊢)○𝔽˜⟜×⊸∾¨(<1+𝕩)×⥊↕2¨𝕩} Run online! The solution is a function that takes n as the left argument (𝕨) and A as the right argument (𝕩). k is just the le...
BQN, 15 bytesSBCS {𝕨(1+⊢𝕊-)⟜𝕩⍟>0} Run online! A block function that takes $t_1$ as the left argument 𝕨 and $t_2$ as the right argument 𝕩. In BQN, 𝕊 indicates recursion on the current block ...
Scala, 83 bytes x=>x.init#::Stream.iterate(x)(x=>x++(x,x.tail).zipped.map(_-_))indexWhere(_.last<1) Try it online! Takes input as a list of two numbers. The fact that the length can...
BQN, 8 bytesSBCS ∾⊒˜¨⊔○∾⊢ Run online! and parsing diagram The idea here is to build a list of groups, with group i containing the ith character of each string that has one, then join the group...
Jq, 19 bytes def s:[range(.)|s];
Python 3, 64 bytes def f(n): z=[n] while n>1:n=int(n**((n+.5)%2));z+=n, return z Try it online!