21181764 has 12 divisors (see below), whose sum is σ = 49424144. Its totient is φ = 7060584.

The previous prime is 21181739. The next prime is 21181777. The reversal of 21181764 is 46718112.

It is a tau number, because it is divible by the number of its divisors (12).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 882562 + ... + 882585.

Almost surely, 2^21181764 is an apocalyptic number.

It is an amenable number.

21181764 is an abundant number, since it is smaller than the sum of its proper divisors (28242380).

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

21181764 is a wasteful number, since it uses less digits than its factorization.

21181764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1765154 (or 1765152 counting only the distinct ones).

The product of its digits is 2688, while the sum is 30.

The square root of 21181764 is about 4602.3650441920. The cubic root of 21181764 is about 276.6861211139.

Adding to 21181764 its reverse (46718112), we get a palindrome (67899876).

It can be divided in two parts, 21181 and 764, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21181764 in words is "twenty-one million, one hundred eighty-one thousand, seven hundred sixty-four".