21907813 has 2 divisors, whose sum is σ = 21907814. Its totient is φ = 21907812.

The previous prime is 21907763. The next prime is 21907829. The reversal of 21907813 is 31870912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20223009 + 1684804 = 4497^2 + 1298^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21907813 is a prime.

It is equal to p_1383763 and since 21907813 and 1383763 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21907013) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10953906 + 10953907.

It is an arithmetic number, because the mean of its divisors is an integer number (10953907).

Almost surely, 2^21907813 is an apocalyptic number.

It is an amenable number.

21907813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21907813 is an equidigital number, since it uses as much as digits as its factorization.

21907813 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 21907813 is about 4680.5782762390. The cubic root of 21907813 is about 279.8120039070.

The spelling of 21907813 in words is "twenty-one million, nine hundred seven thousand, eight hundred thirteen".