21151764 has 18 divisors (see below), whose sum is σ = 53467050. Its totient is φ = 7050576.

The previous prime is 21151747. The next prime is 21151783. The reversal of 21151764 is 46715112.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 11492100 + 9659664 = 3390^2 + 3108^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 293739 + ... + 293810.

Almost surely, 2^21151764 is an apocalyptic number.

It is an amenable number.

21151764 is an abundant number, since it is smaller than the sum of its proper divisors (32315286).

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

21151764 is a wasteful number, since it uses less digits than its factorization.

21151764 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 587559 (or 587554 counting only the distinct ones).

The product of its digits is 1680, while the sum is 27.

The square root of 21151764 is about 4599.1046954815. The cubic root of 21151764 is about 276.5554347137. Note that the first 3 decimals are identical.

Adding to 21151764 its reverse (46715112), we get a palindrome (67866876).

The spelling of 21151764 in words is "twenty-one million, one hundred fifty-one thousand, seven hundred sixty-four".