21543957 has 6 divisors (see below), whose sum is σ = 31119062. Its totient is φ = 14362632.

The previous prime is 21543931. The next prime is 21543961. The reversal of 21543957 is 75934512.

21543957 is a `hidden beast` number, since 21 + 543 + 95 + 7 = 666.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 1347921 = 4494^2 + 1161^2 .

It is not a de Polignac number, because 21543957 - 2⁷ = 21543829 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21543757) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1196878 + ... + 1196895.

Almost surely, 2^21543957 is an apocalyptic number.

It is an amenable number.

21543957 is a deficient number, since it is larger than the sum of its proper divisors (9575105).

21543957 is a wasteful number, since it uses less digits than its factorization.

21543957 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2393779 (or 2393776 counting only the distinct ones).

The product of its digits is 37800, while the sum is 36.

The square root of 21543957 is about 4641.5468326841. The cubic root of 21543957 is about 278.2542616252.

It can be divided in two parts, 215439 and 57, that added together give a triangular number (215496 = T₆₅₆).

The spelling of 21543957 in words is "twenty-one million, five hundred forty-three thousand, nine hundred fifty-seven".