21381556 has 12 divisors (see below), whose sum is σ = 42763168. Its totient is φ = 9163512.

The previous prime is 21381553. The next prime is 21381557. The reversal of 21381556 is 65518312.

21381556 is an admirable number.

It is a super-2 number, since 2×21381556² = 914341873962272, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21381553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 381786 + ... + 381841.

Almost surely, 2^21381556 is an apocalyptic number.

It is an amenable number.

21381556 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21381556 is a wasteful number, since it uses less digits than its factorization.

21381556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 763638 (or 763636 counting only the distinct ones).

The product of its digits is 7200, while the sum is 31.

The square root of 21381556 is about 4624.0194636269. The cubic root of 21381556 is about 277.5533257907.

Adding to 21381556 its reverse (65518312), we get a palindrome (86899868).

The spelling of 21381556 in words is "twenty-one million, three hundred eighty-one thousand, five hundred fifty-six".