Combining Streams of substrings

I have the following code that iterates over Java DateTimeFormatter pattern combinations of "E".."EEEE" and "M".."MMMM".

My question is, is there an idiomatic (or just 'more idiomatic') way to use Java Streams in this case?

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class DateTimeFormattingStackOverflow {
    static LocalDateTime dateTime = LocalDateTime.now();

    static Stream<String> substrings(String str) {
        return IntStream.range(1, str.length() + 1)
                .mapToObj(i -> str.substring(0, i));
    }

    static void printDateTime(String pattern) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern(pattern);
        System.out.println(pattern + ", " + dtf.format(dateTime));
    }

    public static void main(String[] args) {
        Stream<String> patterns = substrings("EEEE")
                .flatMap(e -> substrings("MMMM").map(m -> e + " " + m))
                .map(em -> em + " d");

        patterns.forEach(DateTimeFormattingStackOverflow::printDateTime);
    }
}

Output

E M d, Sat 7 1
E MM d, Sat 07 1
E MMM d, Sat Jul 1
E MMMM d, Sat July 1
EE M d, Sat 7 1
EE MM d, Sat 07 1
EE MMM d, Sat Jul 1
EE MMMM d, Sat July 1
...