21131507 has 2 divisors, whose sum is σ = 21131508. Its totient is φ = 21131506.

The previous prime is 21131489. The next prime is 21131519. The reversal of 21131507 is 70513112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21131507 - 2⁸ = 21131251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21131567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10565753 + 10565754.

It is an arithmetic number, because the mean of its divisors is an integer number (10565754).

Almost surely, 2^21131507 is an apocalyptic number.

21131507 is a deficient number, since it is larger than the sum of its proper divisors (1).

21131507 is an equidigital number, since it uses as much as digits as its factorization.

21131507 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 210, while the sum is 20.

The square root of 21131507 is about 4596.9018914917. The cubic root of 21131507 is about 276.4671209952.

Adding to 21131507 its reverse (70513112), we get a palindrome (91644619).

The spelling of 21131507 in words is "twenty-one million, one hundred thirty-one thousand, five hundred seven".