Skip to content

Instantly share code, notes, and snippets.

@joriki
Created December 28, 2023 23:04
Show Gist options
  • Save joriki/08085c75cfb627c400104a00236f5cd0 to your computer and use it in GitHub Desktop.
Save joriki/08085c75cfb627c400104a00236f5cd0 to your computer and use it in GitHub Desktop.
find palindromic U-shaped triangular arrays in OEIS; see https://math.stackexchange.com/questions/4835012
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.math.BigInteger;
public class OEISScanner {
public static void main (String [] args) throws IOException {
// OEIS sequence data downloaded from https://oeis.org/stripped.gz
BufferedReader reader = new BufferedReader (new FileReader (args [0]));
outer:
for (;;) {
String line = reader.readLine();
if (line == null)
break;
if (line.startsWith("#"))
continue;
int space = line.indexOf(' ');
String name = line.substring(0,space);
String [] terms = line.substring(space + 2).split(",");
boolean changed = false;
for (int n = 1,i = 0;;n++) {
int next = i + n;
if (next > terms.length)
break;
BigInteger last = null;
for (int j = 0;j <= n - j - 1;j++) {
if (!terms [i + j].equals(terms [i + n - j - 1]))
continue outer;
try {
BigInteger value = new BigInteger (terms [i + j]).abs();
if (j != 0) {
if (value.compareTo(last) > 0)
continue outer;
if (!value.equals(last))
changed = true;
}
last = value;
} catch (NumberFormatException nfe) {
continue outer;
}
}
i = next;
}
if (changed)
System.out.println("[" + name + "](https://oeis.org/" + name + ")");
}
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment