21455636842 has 4 divisors (see below), whose sum is σ = 32183455266. Its totient is φ = 10727818420.

The previous prime is 21455636749. The next prime is 21455636869. The reversal of 21455636842 is 24863655412.

It is a happy number.

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

It can be written as a sum of positive squares in only one way, i.e., 21269013921 + 186622921 = 145839^2 + 13661^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21455636792 and 21455636801.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5363909209 + ... + 5363909212.

Almost surely, 2^21455636842 is an apocalyptic number.

21455636842 is a deficient number, since it is larger than the sum of its proper divisors (10727818424).

21455636842 is a wasteful number, since it uses less digits than its factorization.

21455636842 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10727818423.

The product of its digits is 1382400, while the sum is 46.

The spelling of 21455636842 in words is "twenty-one billion, four hundred fifty-five million, six hundred thirty-six thousand, eight hundred forty-two".