'Nummer' is feminine, therefore 'eine' is the appropriate indefinite article. And remember to capitalize your nouns.
die Mathematik http://dictionary.reverso.net/german-english/mathematik
The number 1 when used for counting or in math is "eins" http://german.about.com/library/anfang/blanfang07.htm
The article ein/ein/eine/eine (masculine/neuter/feminine/plural) means "a", "an", or "one" as describing a noun. http://german.about.com/library/anfang/blanfang03.htm
It was in Michigan, USA. I don't remember whether it was just me and my siblings who said this or whether our friends did it too.
I should add we had a grandfather who immigrated (by himself!) at age 13 (1889) from Germany. This may well be where we learned it, although I don't remember HIM ever saying it. I don't remember whether it was just me and my siblings or whether our friends did it too.
He used very little German in front of us, although he regularly said, "Schlafen sie wohl!" at bedtime when we visited. The only other German I remember hearing from him was a table grace: "Komm' lieber Herr Jesu/ Sei unser Gast/ Segne alles was du/ Uns bescheren hast." I took German in college (after two years of it in High School - first German class in our town since World War II) and started writing letters to Grandpa "auf Deutsch". By then he was a very old man, and he seemed so pleased by this. I struggled with his handwriting when he wrote back - the handwriting he had learned as a child was very different from the handwriting he used to write English, which was the common English cursive. But he wrote German in Fraktur (which is spiky - reminded me of an electrocardiogram). One of my German profs was kind enough to help me decipher the Fraktur. I have just googled "Fraktur handwriting" and found some examples - you may not think this is as hard to read as I indicated, but remember his writing had the added shakiness of an old man in his late 80's, then early 90's.
Please express why this sentence does not make sense. It makes perfect sense to me.
"Eine" is either "a" or "an" for feminine or plural nouns. In English, "an" is only used before a vowel sound. "Ein" is either "a" or "an" also, but is for Masculine or Neuter nouns in Nominative case and Neuter nouns in Accusative case. Masculine nouns in Accusative case use "einen". http://german.about.com/library/blcase_sum.htm
Adjectives change endings for number (singular and plural), gender (masculine, neuter, feminine) and case (Nominative, Accusative, Dative, Genitive).