How do I write in Hebrew for a Ketbuah, “On the first day of the week, the thirtieth day of Adar I in the year fifty-seven seventy one”

Question

Question was asked by Stephen Spiegel, I'm just posting it here as its own question instead of a comment.

Answer 1

Assuming it's a leap year (i.e. there's both Adar I and Adar II),

בראשון בשבת שלושים יום לחדש אדר הראשון שהוא ראש חודש לאדר השני שנת חמשת אלפים ושבע מאות ושבעים ואחד