21407551 has 4 divisors (see below), whose sum is σ = 23353704. Its totient is φ = 19461400.

The previous prime is 21407543. The next prime is 21407557. The reversal of 21407551 is 15570412.

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

It is a cyclic number.

It is not a de Polignac number, because 21407551 - 2³ = 21407543 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21407557) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 973060 + ... + 973081.

It is an arithmetic number, because the mean of its divisors is an integer number (5838426).

Almost surely, 2^21407551 is an apocalyptic number.

21407551 is a deficient number, since it is larger than the sum of its proper divisors (1946153).

21407551 is a wasteful number, since it uses less digits than its factorization.

21407551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1946152.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 21407551 is about 4626.8294760019. The cubic root of 21407551 is about 277.6657603388.

Adding to 21407551 its reverse (15570412), we get a palindrome (36977963).

The spelling of 21407551 in words is "twenty-one million, four hundred seven thousand, five hundred fifty-one".