21001000 has 32 divisors (see below), whose sum is σ = 49144680. Its totient is φ = 8400000.

The previous prime is 21000983. The next prime is 21001021. The reversal of 21001000 is 10012.

It can be written as a sum of positive squares in 4 ways, for example, as 3511876 + 17489124 = 1874^2 + 4182^2 .

It is a Harshad number since it is a multiple of its sum of digits (4).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9501 + ... + 11500.

Almost surely, 2^21001000 is an apocalyptic number.

21001000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001000 is an abundant number, since it is smaller than the sum of its proper divisors (28143680).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21001000 is a wasteful number, since it uses less digits than its factorization.

21001000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21022 (or 21008 counting only the distinct ones).

The product of its (nonzero) digits is 2, while the sum is 4.

The square root of 21001000 is about 4582.6848026021. The cubic root of 21001000 is about 275.8967968133.

Adding to 21001000 its reverse (10012), we get a palindrome (21011012).

The spelling of 21001000 in words is "twenty-one million, one thousand".