Hacker News, but only the items with prime IDs.
Every item on Hacker News has a unique numeric ID. This site filters HN to show only items where that ID is a prime number. Out of ~43 million HN items, about 2.7 million have prime IDs.
Beyond just primes, we classify items by special prime categories:
| Filter | Description | Count |
|---|---|---|
| Mersenne | Primes of form 2^p - 1 | 7 |
| Fermat | Primes of form 2^(2^n) + 1 | 5 |
| Sophie Germain | p where 2p+1 is also prime | ~100k |
| Palindrome | Reads same forwards/backwards | 781 |
| p^k+e | Various power-plus-offset forms | varies |
One of the most fascinating discoveries: palindromic primes essentially stop at 10 million.
We found exactly 781 palindromic primes under 50 million, with the largest being 9,989,899.
It comes down to the divisibility rule for 11:
A number is divisible by 11 if its alternating digit sum equals zero.
For any even-digit palindrome like ABCDDCBA:
A - B + C - D + D - C + B - A = 0
This means all even-digit palindromes are divisible by 11, and therefore not prime (except 11 itself).
So palindromic primes can only have an odd number of digits: 1, 3, 5, or 7 digits. The 7-digit palindromic primes max out at 9,989,899.
The next palindromic prime would need 9 digits (over 100 million), far beyond HN's current item count.
This means we've captured all palindromic prime HN items that will ever exist for the foreseeable future!
The bulk of the data comes from the HN BigQuery dataset which contains the full history of Hacker News items.
We export the data, filter for prime IDs using a sieve, and store in sharded SQLite databases for client-side querying. Live data beyond our snapshot comes from the HN Firebase API.
- Frontend: Pure HTML/JS with SQLite WASM for client-side queries
- Data: Sharded SQLite databases (~50k items per shard)
- ETL: Node.js script with prime sieve and special prime classification
- Jump-to-Prime: Uses prime counting function estimators (PNT, Legendre, Li) with iterative refinement
- Live Mode: Fetches recent items from HN Firebase API when browsing beyond the database
The "jump to ID" feature uses the Prime Number Theorem to estimate which page contains a given ID:
- PNT: π(x) ≈ x / ln(x)
- Legendre: π(x) ≈ x / (ln(x) - 1.08366)
- Li: Logarithmic integral asymptotic expansion
The iterative probe typically finds the correct page in 2-3 iterations using π(target) - π(landing) correction.
- OEIS A000040 - The prime numbers sequence
- HN Firebase API - Data source