You have already an excellent answer from Del_icious_manager as usual.
Your previous question (METROPOLITAN OPERA QUIZ) and this one reminded me the following old puzzle, published in one of Martin Gardner's books on recreational mathematics: 'J.F. Kennedy was born in 1917, was elected as U.S. President in 1960. His book 'Profiles in courage' was published when he was 46, in his 3rd year in office. The sum
1917 + 1960 + 46 + 3 = 3926
Charles de Gaulle was born in 1890, was elected as President of France in 1958 and when he was 73 years old, he has been in office for 5 years.The sum
1890 + 1958 + 73 + 5 = 3926.
How to explain that remarkable coincidence?'
Explanation: if we take an arbitrary date and add to it the number of years to a particular following date (1963 in the puzzle), we'll simply get that second date. Also, for any 4 numbers a, b, c, d we have
a + b + c + d = a + c + b + d = (a + c) + (b + d), so
1917 + 1960 + 46 + 3 = (1917 + 46) + (1960 + 3) = 2 * 1963 = 3926
1890 + 1958 + 73 + 5 = (1890 + 73) + (1958 + 5) = 2 * 1963 = 3926
So, there is nothing remarkable and it is quite trivial!
Now from your equation and above notes we can conclude that either:
a) if the person has celebrated a birthday in the year of his death, then the number of compositions is equal to his century year of birth, or
b) otherwise the number of compositions is equal to his century year of birth plus one (as is the case in Del_icious_manager's answer - Wagner hadn't entered his 70th year yet when he died in February 1883, being born in May 1813 - by the way I also didn't know about 'Die Hochzeit')
May I suggest to the public in CM Forum a puzzle with some arithmetic involved too? Recall that an integer number, being a product of some integer and itself is called 'perfect square', for example
64 = 8 * 8 = 8² and 64 is a perfect square (imagine 8 x 8 chessboard).
But 64 = 4 * 4 * 4 = 4³, so 64 is also a perfect cube, finally
64 = 2 * 2 * 2 * 2 * 2 * 2 = 2⁶ is simultaneously a perfect 6th power.
Now the puzzle, it is very easy: identify the composer by the following:
1) The number of symphonies he has written is a perfect square;
2) The Opus number of his last symphony is a perfect cube;
3) The number of his string quartets is a perfect 4th power;
4) The number of his piano sonatas is a perfect 5th power;
5) The number of his operas is simultaneously a perfect 2nd, 3rd, 4th and 5th power.
I am sure no hints are necessary, happy solving!