Generating US routing number (ABA RTN) in Finance provider.

src/main/java/net/datafaker/providers/base/Finance.java

@@ -1,7 +1,11 @@
 package net.datafaker.providers.base;
 
 import java.math.BigInteger;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
 import java.util.regex.Pattern;
 
 /**
@@ -92,6 +96,25 @@ public String iban(String countryCode) {
         return countryCode + checkSum + basicBankAccountNumber;
     }
 
+    public String usRoutingNumber() {
+        String base =
+            // 01 through 12 are the "normal" routing numbers, and correspond to the 12 Federal Reserve Banks.
+            String.format("%02d", faker.random().nextInt(12) + 1)
+            + faker.regexify("\\d{6}");
+        int check =
+           Character.getNumericValue(base.charAt(0)) * 3
+            + Character.getNumericValue(base.charAt(1)) * 7
+            + Character.getNumericValue(base.charAt(2))
+            + Character.getNumericValue(base.charAt(3)) * 3
+            + Character.getNumericValue(base.charAt(4)) * 7
+            + Character.getNumericValue(base.charAt(5))
+            + Character.getNumericValue(base.charAt(6)) * 3
+            + Character.getNumericValue(base.charAt(7)) * 7;
+        check = Math.abs(check % 10 - 10) % 10;
+
+        return base + check;
+    }
+
     private CreditCardType randomCreditCardType() {
         return CreditCardType.values()[this.faker.random().nextInt(CreditCardType.values().length)];
     }

src/test/java/net/datafaker/providers/base/FinanceTest.java

@@ -82,4 +82,19 @@ void discoverCard() {
         String creditCard = finance.creditCard(CreditCardType.DISCOVER).replace("-", "");
         assertThat(creditCard).startsWith("6").hasSize(16);
     }
+
+    @RepeatedTest(100)
+    void usRoutingNumber() {
+        String rtn = finance.usRoutingNumber();
+        System.out.println(rtn);
+        assertThat(rtn).matches("\\d{9}");
+        int check = 0;
+        for (int index = 0; index < 3; index++) {
+            int pos = index * 3;
+            check += Character.getNumericValue(rtn.charAt(pos)) * 3;
+            check += Character.getNumericValue(rtn.charAt(pos + 1)) * 7;
+            check += Character.getNumericValue(rtn.charAt(pos + 2));
+        }
+        assertThat(check % 10).isEqualTo(0);
+    }
 }