21351487 has 4 divisors (see below), whose sum is σ = 21475080. Its totient is φ = 21227896.

The previous prime is 21351469. The next prime is 21351503. The reversal of 21351487 is 78415312.

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 21351487 - 2¹⁹ = 20827199 is a prime.

It is a super-2 number, since 2×21351487² = 911771994222338, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351457) 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, 61537 + ... + 61882.

It is an arithmetic number, because the mean of its divisors is an integer number (5368770).

Almost surely, 2^21351487 is an apocalyptic number.

21351487 is a deficient number, since it is larger than the sum of its proper divisors (123593).

21351487 is a wasteful number, since it uses less digits than its factorization.

21351487 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 123592.

The product of its digits is 6720, while the sum is 31.

The square root of 21351487 is about 4620.7669276864. The cubic root of 21351487 is about 277.4231564953.

Adding to 21351487 its reverse (78415312), we get a palindrome (99766799).

The spelling of 21351487 in words is "twenty-one million, three hundred fifty-one thousand, four hundred eighty-seven".