21517191 has 8 divisors (see below), whose sum is σ = 31877360. Its totient is φ = 14344776.

The previous prime is 21517187. The next prime is 21517231. The reversal of 21517191 is 19171512.

It is not a de Polignac number, because 21517191 - 2² = 21517187 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 796933 = 21517191 / (2 + 1 + 5 + 1 + 7 + 1 + 9 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21517591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 398440 + ... + 398493.

It is an arithmetic number, because the mean of its divisors is an integer number (3984670).

Almost surely, 2^21517191 is an apocalyptic number.

21517191 is a deficient number, since it is larger than the sum of its proper divisors (10360169).

21517191 is an equidigital number, since it uses as much as digits as its factorization.

21517191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 796942 (or 796936 counting only the distinct ones).

The product of its digits is 630, while the sum is 27.

The square root of 21517191 is about 4638.6626305434. The cubic root of 21517191 is about 278.1389804192.

The spelling of 21517191 in words is "twenty-one million, five hundred seventeen thousand, one hundred ninety-one".