21355978 has 32 divisors (see below), whose sum is σ = 39426048. Its totient is φ = 8467200.

The previous prime is 21355969. The next prime is 21355987. The reversal of 21355978 is 87955312.

It is an interprime number because it is at equal distance from previous prime (21355969) and next prime (21355987).

It is a self number, because there is not a number n which added to its sum of digits gives 21355978.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13783 + ... + 15253.

It is an arithmetic number, because the mean of its divisors is an integer number (1232064).

Almost surely, 2^21355978 is an apocalyptic number.

21355978 is a deficient number, since it is larger than the sum of its proper divisors (18070070).

21355978 is a wasteful number, since it uses less digits than its factorization.

21355978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1558.

The product of its digits is 75600, while the sum is 40.

The square root of 21355978 is about 4621.2528604265. The cubic root of 21355978 is about 277.4426058831.

The spelling of 21355978 in words is "twenty-one million, three hundred fifty-five thousand, nine hundred seventy-eight".