Answer:
Good question. Sylvanus is another name for Silas; see commentary below:
2 Co 1:19. Silvanus; full name for Silas, who is often mentioned in the Acts as Paul’s companion in labor and suffering.
Here are other places it mentions the name of Sylvanus:
2 Corinthians 1:19 For the Son of God, Jesus Christ, who was preached among you by us, even by me and Silvanus and Timotheus, was not yea and nay, but in him was yea.
1 Thessalonians 1:1 Paul, and Silvanus, and Timotheus, unto the church of the Thessalonians which is in God the Father and in the Lord Jesus Christ: Grace be unto you, and peace, from God our Father, and the Lord Jesus Christ.
2 Thessalonians 1:1 Paul, and Silvanus, and Timotheus, unto the church of the Thessalonians in God our Father and the Lord Jesus Christ:
1 Peter 5:12 By Silvanus, a faithful brother unto you, as I suppose, I have written briefly, exhorting, and testifying that this is the true grace of God wherein ye stand.
Here is where it mentions Silas (same person):
Acts 15:22 Then pleased it the apostles and elders, with the whole church, to send chosen men of their own company to Antioch with Paul and Barnabas; namely, Judas surnamed Barsabas, and Silas, chief men among the brethren:
Acts 15:27 We have sent therefore Judas and Silas, who shall also tell you the same things by mouth.
Acts 15:32 And Judas and Silas, being prophets also themselves, exhorted the brethren with many words, and confirmed them.
Acts 15:34 Notwithstanding it pleased Silas to abide there still.
Acts 15:40 And Paul chose Silas, and departed, being recommended by the brethren unto the grace of God.
Acts 16:19 And when her masters saw that the hope of their gains was gone, they caught Paul and Silas, and drew them into the marketplace unto the rulers,
Acts 16:25 And at midnight Paul and Silas prayed, and sang praises unto God: and the prisoners heard them.
Acts 16:29 Then he called for a light, and sprang in, and came trembling, and fell down before Paul and Silas,
Acts 17:4 And some of them believed, and consorted with Paul and Silas; and of the devout Greeks a great multitude, and of the chief women not a few.
Acts 17:10 And the brethren immediately sent away Paul and Silas by night unto Berea: who coming thither went into the synagogue of the Jews.
Acts 17:14 And then immediately the brethren sent away Paul to go as it were to the sea: but Silas and Timotheus abode there still.
Acts 17:15 And they that conducted Paul brought him unto Athens: and receiving a commandment unto Silas and Timotheus for to come to him with all speed, they departed.
Acts 18:5 And when Silas and Timotheus were come from Macedonia, Paul was pressed in the spirit, and testified to the Jews that Jesus was Christ.
Pastor Brad