21739517 has 2 divisors, whose sum is σ = 21739518. Its totient is φ = 21739516.

The previous prime is 21739513. The next prime is 21739537. The reversal of 21739517 is 71593712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15912121 + 5827396 = 3989^2 + 2414^2 .

It is a cyclic number.

It is not a de Polignac number, because 21739517 - 2² = 21739513 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21739513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10869758 + 10869759.

It is an arithmetic number, because the mean of its divisors is an integer number (10869759).

Almost surely, 2^21739517 is an apocalyptic number.

It is an amenable number.

21739517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21739517 is an equidigital number, since it uses as much as digits as its factorization.

21739517 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13230, while the sum is 35.

The square root of 21739517 is about 4662.5654955185. The cubic root of 21739517 is about 279.0936552613.

The spelling of 21739517 in words is "twenty-one million, seven hundred thirty-nine thousand, five hundred seventeen".