By the Numbers (Hard Mode)

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Across
  1. 4. Sequence where each term is the sum of the previous two
  2. 6. Alternative to degrees for measuring angles
  3. 17. Irrational constant approximated by 1.618
  4. 20. Having the same size and shape
  5. 21. Study of spaces that deform without tearing
  6. 22. Transform used for differential equations
  7. 24. Mathematician behind a famous formula linking e, i, and π
  8. 26. Inventor of calculus (independently of Leibniz)
  9. 28. Step-by-step computational procedure
  10. 30. Triangle guy, or unit of pressure
  11. 31. Non-orientable surface with no boundary
  12. 32. Donut-shaped surface
  13. 34. Degree-2 polynomial
  14. 36. Quadrilateral with equal sides but not necessarily right angles
  15. 37. Where a function or spacetime "blows up"
  16. 38. Multiplier of a variable in algebra
Down
  1. 1. Larger than any number
  2. 2. Curve described by y = ax² + bx + c
  3. 3. Describes position in a sequence
  4. 5. Expression with two terms
  5. 7. A curve’s forever companion, never touching
  6. 8. Average of squared deviations
  7. 9. Expansion technique for functions near a point
  8. 10. Balanced proportions or invariance under transformation
  9. 11. Longest side in a right triangle
  10. 12. Product of consecutive integers down to 1
  11. 13. Expression with many terms
  12. 14. Inverse operation of exponentiation
  13. 15. Function tied to the distribution of prime numbers
  14. 16. Line joining non-adjacent vertices
  15. 18. Scalar showing how a linear transformation stretches a vector
  16. 19. Surface with only one side
  17. 23. Structure-preserving mapping in algebra
  18. 25. Famous misspelling of a hypothesis (trick clue for RIEMANN)
  19. 27. Oval conic section
  20. 29. Pioneer of set theory and infinity paradoxes
  21. 33. Mean where reciprocals are averaged
  22. 35. Chain-based probabilistic model