"Mahna Mahna" doesn't seem to be the right transliteration. "Muhnummina" seems better to me. But it doesn't matter. Not after all of these years. Apparently, Wikipedia thinks it should be written, "Mah Nà Mah Nà:"
On 30 November, 1969, "Mahna Mahna" was performed on the The Ed Sullivan Show by a Muppet also known as Mahna Mahna, and the Snowths. Also in 1969, "Mahna Mahna" was performed on Sesame Street by a character that was later known as Bip Bipadotta, along with two Anything Muppet girls.