## Let $S(n)$ be the sum of all contiguous integer-substrings that can be formed from the integer $n$. The substrings need not be distinct.

For example, $S(2024) = 2 + 0 + 2 + 4 + 20 + 02 + 24 + 202 + 024 + 2024 = 2304$.

Let $P(n)$ be the integer formed by concatenating the first $n$ primes together. For example, $P(7) = 2357111317$.

Let $C(n, k)$ be the integer formed by concatenating $k$ copies of $P(n)$ together. For example, $C(7, 3) = 235711131723571113172357111317$.

Evaluate $S(C(10^6, 10^{12})) \bmod (10^9 + 7)$.

### To solve this problem, we will break it down into smaller steps and implement each step using Python code. Here’s a step-by-step solution:

Step 1: Generating Prime Numbers

First, we need a way to generate prime numbers. We can use the Sieve of Eratosthenes algorithm to efficiently generate all prime numbers up to a given limit.

“`python

def generate_primes(limit):

is_prime = [True] * (limit + 1)

is_prime[0] = is_prime[1] = False

for i in range(2, int(limit ** 0.5) + 1):

if is_prime[i]:

for j in range(i * i, limit + 1, i):

is_prime[j] = False

primes = [i for i in range(limit + 1) if is_prime[i]]

return primes

“`

Step 2: Concatenating Primes

Next, we need a function to concatenate the first `n` primes together.

“`python

def concatenate_primes(n, primes):

concatenated = “”

for i in range(n):

concatenated += str(primes[i])

return int(concatenated)

“`

Step 3: Concatenating Prime Multiples

We also need a function to concatenate `k` copies of the first `n` primes together.

“`python

def concatenate_prime_multiples(n, k, primes):

concatenated = “”

for i in range(k):

concatenated += str(concatenate_primes(n, primes))

return int(concatenated)

“`

Step 4: Finding Contiguous Integer-Substrings

To find all contiguous integer-substrings, we can convert the number to a string and iterate through all possible substrings.

“`python

def find_integer_substrings(num):

num_str = str(num)

substrings = []

for i in range(len(num_str)):

for j in range(i + 1, len(num_str) + 1):

substr = int(num_str[i:j])

substrings.append(substr)

return substrings

“`

Step 5: Summing the Integer-Substrings

Finally, we can sum all the integer-substrings and calculate the modulo.

“`python

def sum_integer_substrings(num):

substrings = find_integer_substrings(num)

return sum(substrings) % (10**9 + 7)

“`

Putting it all together:

To solve the given problem, we can call the above functions with appropriate arguments.

“`python

primes = generate_primes(10**6)

result = sum_integer_substrings(concatenate_prime_multiples(10**6, 10**12, primes))

print(result)

“`

Note: The code provided above assumes that the `generate_primes` function is given the limit as $10^6$, corresponding to the number of primes required for the calculation. However, the algorithm and code are applicable for any positive integer `limit`. Also, be aware that the code above may take a considerable amount of time to execute due to the large values involved.

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