21001509 has 6 divisors (see below), whose sum is σ = 30335526. Its totient is φ = 14001000.

The previous prime is 21001493. The next prime is 21001523. The reversal of 21001509 is 90510012.

It can be written as a sum of positive squares in only one way, i.e., 14861025 + 6140484 = 3855^2 + 2478^2 .

It is not a de Polignac number, because 21001509 - 2⁴ = 21001493 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21001491 and 21001500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001529) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166742 + ... + 1166759.

It is an arithmetic number, because the mean of its divisors is an integer number (5055921).

Almost surely, 2^21001509 is an apocalyptic number.

It is an amenable number.

21001509 is a deficient number, since it is larger than the sum of its proper divisors (9334017).

21001509 is a wasteful number, since it uses less digits than its factorization.

21001509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2333507 (or 2333504 counting only the distinct ones).

The product of its (nonzero) digits is 90, while the sum is 18.

The square root of 21001509 is about 4582.7403373964. The cubic root of 21001509 is about 275.8990257601.

The spelling of 21001509 in words is "twenty-one million, one thousand, five hundred nine".