21780554 has 4 divisors (see below), whose sum is σ = 32670834. Its totient is φ = 10890276.

The previous prime is 21780533. The next prime is 21780559. The reversal of 21780554 is 45508712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13213225 + 8567329 = 3635^2 + 2927^2 .

It is a super-4 number, since 4×21780554⁴ (a number of 30 digits) contains 4444 as substring.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21780554.

It is not an unprimeable number, because it can be changed into a prime (21780559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5445137 + ... + 5445140.

Almost surely, 2^21780554 is an apocalyptic number.

21780554 is a deficient number, since it is larger than the sum of its proper divisors (10890280).

21780554 is a wasteful number, since it uses less digits than its factorization.

21780554 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10890279.

The product of its (nonzero) digits is 11200, while the sum is 32.

The square root of 21780554 is about 4666.9641095684. The cubic root of 21780554 is about 279.2691569723.

The spelling of 21780554 in words is "twenty-one million, seven hundred eighty thousand, five hundred fifty-four".