21618949 has 24 divisors (see below), whose sum is σ = 25232760. Its totient is φ = 18480000.

The previous prime is 21618943. The next prime is 21618953. The reversal of 21618949 is 94981612.

It can be written as a sum of positive squares in 4 ways, for example, as 3214849 + 18404100 = 1793^2 + 4290^2 .

It is not a de Polignac number, because 21618949 - 2²³ = 13230341 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21618943) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 213999 + ... + 214099.

It is an arithmetic number, because the mean of its divisors is an integer number (1051365).

Almost surely, 2^21618949 is an apocalyptic number.

21618949 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21618949 is a deficient number, since it is larger than the sum of its proper divisors (3613811).

21618949 is a wasteful number, since it uses less digits than its factorization.

21618949 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213 (or 202 counting only the distinct ones).

The product of its digits is 31104, while the sum is 40.

The square root of 21618949 is about 4649.6181563651. The cubic root of 21618949 is about 278.5767446091.

The spelling of 21618949 in words is "twenty-one million, six hundred eighteen thousand, nine hundred forty-nine".