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21000000 = 263567

21000000 has 196 divisors, whose sum is σ = 79373984. Its totient is φ = 4800000.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000000 is 12.

Adding to 21000000 its reverse (12), we get a palindrome (21000012).

It is a Harshad number since it is a multiple of its sum of digits (3).

It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.

It is a nialpdrome in base 10.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 2999997 + ... + 3000003.

Almost surely, 221000000 is an apocalyptic number.

21000000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21000000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39686992).

21000000 is an abundant number, since it is smaller than the sum of its proper divisors (58373984).

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

21000000 is an frugal number, since it uses more digits than its factorization.

21000000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52 (or 17 counting only the distinct ones).

The product of its (nonzero) digits is 2, while the sum is 3.

The square root of 21000000 is about 4582.5756949558. The cubic root of 21000000 is about 275.8924176381.

The spelling of 21000000 in words is "twenty-one million", and thus it is an aban number and an uban number.