Can even numbers become prime? The Sequence

Everyone knows the only even prime number is 2. Ho-hum. But, there are certain even numbers n where, when concatenated with n-1, they become a prime number.

For starters, 1 isn't in the list, because 10 isn't prime. Similarly with 2 (21), and 3 (32). However, 4 works because 43 is prime, so it's the first number in the sequence a(1) = 4. The next number that works (neither 6 (65) nor 8 (87) work) is 10, because 109 is prime, so a(2) = 10. Then we skip a bunch more until 22, because 2221 is prime, so a(3) = 22. And so on.

Obviously all terms in this sequence are even, because any odd number n when concatenated with n-1 becomes even (like 3 turns into 32), which will never be prime.

This is sequence A054211 on OEIS.

The Challenge

Given an input number n that fits somewhere into this sequence (i.e., n concatenated with n-1 is prime), output its position in this sequence. You can choose either 0- or 1-indexed, but please state which in your submission.

Rules


The input and output can be assumed to fit in your language's native integer type.
The input and output can be given in any convenient format.
Either a full program or a function are acceptable. If a function, you can return the output rather than printing it.
If possible, please include a link to an online testing environment so other people can try out your code!
Standard loopholes are forbidden.
This is code-golf so all usual golfing rules apply, and the shortest code (in bytes) wins.


Examples

The below examples are 1-indexed.

n = 4
1

n = 100
11

n = 420
51
Jelly, &nbsp;8&nbsp; 7 bytes

ḊżṖVÆPS


A monadic link taking a sequence member and returning its index in the sequence.

Try it online!

How?

ḊżṖVÆPS - Link: number, n
Ḋ       - dequeue (implicit range) = [ 2   , 3   , 4   ,... ,              n         ]
  Ṗ     - pop (implicit range)     = [   1 ,   2 ,   3 ,... ,                  n-1   ]
 ż      - zip                      = [[2,1],[3,2],[4,3],... ,             [n , n-1]  ]
   V    - evaluate as Jelly code   = [ 21  , 32  , 43  ,... ,         int("n"+"n-1") ]
    ÆP  - is prime? (vectorises)   = [  0  ,  0  ,  1  ,... , isPrime(int("n"+"n-1"))]
      S - sum