21820437 has 6 divisors (see below), whose sum is σ = 31518422. Its totient is φ = 14546952.

The previous prime is 21820429. The next prime is 21820439. The reversal of 21820437 is 73402812.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 531441 = 4614^2 + 729^2 .

It is not a de Polignac number, because 21820437 - 2³ = 21820429 is a prime.

It is a super-2 number, since 2×21820437² = 952262941741938, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21820437.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21820439) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1212238 + ... + 1212255.

Almost surely, 2^21820437 is an apocalyptic number.

It is an amenable number.

21820437 is a deficient number, since it is larger than the sum of its proper divisors (9697985).

21820437 is a wasteful number, since it uses less digits than its factorization.

21820437 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2424499 (or 2424496 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21820437 is about 4671.2350615228. The cubic root of 21820437 is about 279.4395123004.

The spelling of 21820437 in words is "twenty-one million, eight hundred twenty thousand, four hundred thirty-seven".