ID | Description / Title |

**1**
| Multiples of 3 and 5 |

**2**
| Even Fibonacci numbers |

**3**
| Largest prime factor |

**4**
| Largest palindrome product |

**5**
| Smallest multiple |

**6**
| Sum square difference |

**7**
| 10001st prime |

**8**
| Largest product in a series |

**9**
| Special Pythagorean triplet |

**10**
| Summation of primes |

**11**
| Largest product in a grid |

**12**
| Highly divisible triangular number |

**13**
| Large sum |

**14**
| Longest Collatz sequence |

**15**
| Lattice paths |

**16**
| Power digit sum |

**17**
| Number letter counts |

**18**
| Maximum path sum I |

**19**
| Counting Sundays |

**20**
| Factorial digit sum |

**21**
| Amicable numbers |

**22**
| Names scores |

**23**
| Non-abundant sums |

**24**
| Lexicographic permutations |

**25**
| 1000-digit Fibonacci number |

**26**
| Reciprocal cycles |

**27**
| Quadratic primes |

**28**
| Number spiral diagonals |

**29**
| Distinct powers |

**30**
| Digit fifth powers |

**31**
| Coin sums |

**32**
| Pandigital products |

**33**
| Digit cancelling fractions |

**34**
| Digit factorials |

**35**
| Circular primes |

**36**
| Double-base palindromes |

**37**
| Truncatable primes |

**38**
| Pandigital multiples |

**39**
| Integer right triangles |

**40**
| Champernowne's constant |

**41**
| Pandigital prime |

**42**
| Coded triangle numbers |

**43**
| Sub-string divisibility |

**44**
| Pentagon numbers |

**45**
| Triangular, pentagonal, and hexagonal |

**46**
| Goldbach's other conjecture |

**47**
| Distinct primes factors |

**48**
| Self powers |

**49**
| Prime permutations |

**50**
| Consecutive prime sum |