21593917 has 2 divisors, whose sum is σ = 21593918. Its totient is φ = 21593916.

The previous prime is 21593879. The next prime is 21593947. The reversal of 21593917 is 71939512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17884441 + 3709476 = 4229^2 + 1926^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21593917 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21593947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10796958 + 10796959.

It is an arithmetic number, because the mean of its divisors is an integer number (10796959).

Almost surely, 2^21593917 is an apocalyptic number.

It is an amenable number.

21593917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21593917 is an equidigital number, since it uses as much as digits as its factorization.

21593917 is an evil number, because the sum of its binary digits is even.

The product of its digits is 17010, while the sum is 37.

The square root of 21593917 is about 4646.9255427648. The cubic root of 21593917 is about 278.4691842429.

Subtracting 21593917 from its reverse (71939512), we obtain a triangular number (50345595 = T₁₀₀₃₄).

The spelling of 21593917 in words is "twenty-one million, five hundred ninety-three thousand, nine hundred seventeen".