21019517 has 4 divisors (see below), whose sum is σ = 21375840. Its totient is φ = 20663196.

The previous prime is 21019487. The next prime is 21019541. The reversal of 21019517 is 71591012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21019517 - 2⁸ = 21019261 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21019597) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 178073 + ... + 178190.

It is an arithmetic number, because the mean of its divisors is an integer number (5343960).

Almost surely, 2^21019517 is an apocalyptic number.

It is an amenable number.

21019517 is a deficient number, since it is larger than the sum of its proper divisors (356323).

21019517 is an equidigital number, since it uses as much as digits as its factorization.

21019517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 356322.

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21019517 is about 4584.7046796931. The cubic root of 21019517 is about 275.9778608931.

The spelling of 21019517 in words is "twenty-one million, nineteen thousand, five hundred seventeen".