There are several ways to increment a variable in bash:
# one way
a=$((a+1))
# or even just
((a++))
# using "let"
let "a=a + 1"
Answering your comment, you could do
${name1}_$((a++))
or
${name1}_$((++a))
depending on whether you wanted to increment the variable before or after echo
ing it.