21149991 has 12 divisors (see below), whose sum is σ = 31681832. Its totient is φ = 14099832.

The previous prime is 21149987. The next prime is 21149993. The reversal of 21149991 is 19994112.

It is not a de Polignac number, because 21149991 - 2² = 21149987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21149993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 43276 + ... + 43761.

Almost surely, 2^21149991 is an apocalyptic number.

21149991 is a deficient number, since it is larger than the sum of its proper divisors (10531841).

21149991 is an frugal number, since it uses more digits than its factorization.

21149991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87052 (or 87040 counting only the distinct ones).

The product of its digits is 5832, while the sum is 36.

The square root of 21149991 is about 4598.9119365346. The cubic root of 21149991 is about 276.5477072812.

The spelling of 21149991 in words is "twenty-one million, one hundred forty-nine thousand, nine hundred ninety-one".