21145709 has 16 divisors (see below), whose sum is σ = 23625840. Its totient is φ = 18800640.

The previous prime is 21145699. The next prime is 21145741. The reversal of 21145709 is 90754112.

It can be written as a sum of positive squares in 8 ways, for example, as 1387684 + 19758025 = 1178^2 + 4445^2 .

It is a cyclic number.

It is not a de Polignac number, because 21145709 - 2¹⁶ = 21080173 is a prime.

It is a super-2 number, since 2×21145709² = 894282018225362, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21145769) 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 15 ways as a sum of consecutive naturals, for example, 51497 + ... + 51905.

It is an arithmetic number, because the mean of its divisors is an integer number (1476615).

Almost surely, 2^21145709 is an apocalyptic number.

It is an amenable number.

21145709 is a deficient number, since it is larger than the sum of its proper divisors (2480131).

21145709 is a wasteful number, since it uses less digits than its factorization.

21145709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 560.

The product of its (nonzero) digits is 2520, while the sum is 29.

The square root of 21145709 is about 4598.4463680682. The cubic root of 21145709 is about 276.5290428570.

The spelling of 21145709 in words is "twenty-one million, one hundred forty-five thousand, seven hundred nine".