21911988 has 24 divisors (see below), whose sum is σ = 58432192. Its totient is φ = 6260544.

The previous prime is 21911987. The next prime is 21912013. The reversal of 21911988 is 88911912.

It is a super-2 number, since 2×21911988² = 960270436224288, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21911987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 130345 + ... + 130512.

Almost surely, 2^21911988 is an apocalyptic number.

21911988 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21911988 is an abundant number, since it is smaller than the sum of its proper divisors (36520204).

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

21911988 is a wasteful number, since it uses less digits than its factorization.

21911988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 260871 (or 260869 counting only the distinct ones).

The product of its digits is 10368, while the sum is 39.

The square root of 21911988 is about 4681.0242468930. The cubic root of 21911988 is about 279.8297774887.

It can be divided in two parts, 2 and 1911988, that added together give a triangular number (1911990 = T₁₉₅₅).

The spelling of 21911988 in words is "twenty-one million, nine hundred eleven thousand, nine hundred eighty-eight".