# Tag Info

18 Steps ...
• 3,401

### Construct a pentagon avoiding compass use

2 circles, 13 lines, 17 points Try it on GeoGebra Let circle(A, B) intersect circle(B, A) at C and D. Let AB intersect circle(A, B) again at E. Let AB intersect circle(B, A) again at F. Let AD ...
• 39.7k

### (-a) × (-a) = a × a

18 steps Different from the already posted 18-step solution. ...
• 390

### Machine Learning Golf: Multiplication

21 13 11 9 weights This is based on the polarization identity of bilinear forms which in the one dimensional real case reduces to the polynomial identity: $$x\cdot y = \frac{(x+y)^2 - (x-y)^2}{4}$$ ...
• 43.8k

### Is this number an exact power of -2: (Very) Hard Mode

C++, 15 operations I have no idea why while loops are allowed as they destroy the whole challenge. Here is an answer without any: ...
• 39.1k

• 39.7k
Accepted

### Google's doodle on kids coding: shortest program solving all the levels

Not my answer 6 blocks The user Alex found a shorter solution, of length 6. I can confirm that their solution works: O(O(Br G G, 6) Br, 5) They attempted to ...

7 weights ...
• 145k

### (-a) × (-a) = a × a

29 26 Steps No lemmas! Comment if you see anything wrong. (It's very easy to make a mistake) ...
• 11.6k

671 ...
• 39.7k

### Is this number an exact power of -2: (Very) Hard Mode

Python 2, 3 operations def f(n): while n>>1: while n&1:return 0 n=n/-2 return n Try it online! The operations are ...
• 145k

### Drive a hexadecimal 7-segment display using NAND logic gates

30 NANDs I am quite sure there are no simpler solutions to this problem, except perhaps by changing the symbols on the display, but that would be another and different problem. Since this is actually ...
• 711

### (-a) × (-a) = a × a

18 steps Not the first 18-step proof, but it’s simpler than the others. ...
• 39.7k

### Machine Learning Golf: Multiplication

33 31 weights ...
• 15.7k

30 fractions ...
• 10.5k

### Construct a pentagon avoiding compass use

7 6 circles, 3 lines This is a classical pentagon construction, a proof of its correctness can be found here.
• 43.8k

### Shortest "arithmetic" formula to output 1000 primes

Score 1164 883 835 772 601 574 554 506 ...
• 39.7k

### Shortest "arithmetic" formula to output 1000 primes

Score 424 193 ...

### Tribute to John Conway: Collatz in FRACTRAN

9 fractions 13/11 22/39 1/13 7/5 320/21 1024/7 3/4 5/6 22/3 Try it online! Input is a power of 2. It's probably easier to think about FRACTRAN code in terms of ...
• 145k
Accepted

### Build a multiplying machine using NAND logic gates

39 gates I am quite sure there are no simpler designs than mine here. It was very difficult to make. I make other minimal circuits too. Transmission delay is indicated by downward position of each ...
• 711

23 steps ...
• 393

### Hexcellent Minesweeping

7 5 vertices, 14 10 edges (Graph made with this online tool and paint.) A-F are our six nodes, and ...
• 26.2k

### Machine Learning Golf: Multiplication

43 weights The two solutions posted so far have been very clever but their approaches likely won't work for more traditional tasks in machine learning (like OCR). Hence I'd like to submit a 'generic' ...

### SKI calculus golf: Half of a Church numeral

40 combinators S(S(SI(K(S(S(KS)K)(K(S(S(KS)(S(KK)S))(K(S(KK)(S(S(KS)K)))))))))(K(S(SI(K(KI)))(K(KI)))))(KK) Try it online! Generated with a little help from a ...
• 39.7k

### Make 1s using a bunch of 1s

By hand -  118 112 111  82 $$(1+(1+1)^{(1+1)^{1+1}}(1+(1+1)(1+(1+(1+1)^{1+1})^{1+1})^{1+1}))(1+(1+1+(1+1+1)^{1+1})(1+1+(((1+1)(1+1+1))^{1+1})^{1+1+1}))$$ Try it at Wolfram Alpha This was ...
• 108k

Score = 192 ...
• 39.7k

### Final tribute to John Conway: FRACTRAN self-interpreter

24 fractions \frac{2}{3}, \frac{5}{7}, \frac{7^{12} 41}{5^{12} 23}, \frac{7^{13}}{5^{13} 37}, \frac{3^{10} 7^3 13}{5^{13} 31}, \frac{3^2 7^{11} 19^1 41}{2^2 5^{11} 29}, \frac{3^3 7^{10} 19^1 23}{2^3 ...
• 719