21012009 has 8 divisors (see below), whose sum is σ = 28544832. Its totient is φ = 13743600.

The previous prime is 21011981. The next prime is 21012053. The reversal of 21012009 is 90021012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21012009 - 2¹² = 21007913 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21012059) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 65917 + ... + 66234.

It is an arithmetic number, because the mean of its divisors is an integer number (3568104).

Almost surely, 2^21012009 is an apocalyptic number.

It is an amenable number.

21012009 is a deficient number, since it is larger than the sum of its proper divisors (7532823).

21012009 is a wasteful number, since it uses less digits than its factorization.

21012009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132207.

The product of its (nonzero) digits is 36, while the sum is 15.

The square root of 21012009 is about 4583.8857970067. The cubic root of 21012009 is about 275.9449979665.

The spelling of 21012009 in words is "twenty-one million, twelve thousand, nine".