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The more official document:
http://www.eduardpankov.ru/laws/cstatus/csts17.shtml
Quote:
В случае, если по желанию матери, не состоящей в браке с отцом ребенка, сведения об отце ребенка не вносятся...

When father's name is not known or cannot be used for some reason, patronymic can be assigned arbitrarily, I guess. And it can even be officially changed (as well as first and family name). I have...