21829978 has 4 divisors (see below), whose sum is σ = 32744970. Its totient is φ = 10914988.

The previous prime is 21829961. The next prime is 21829979. The reversal of 21829978 is 87992812.

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., 13344409 + 8485569 = 3653^2 + 2913^2 .

It is not an unprimeable number, because it can be changed into a prime (21829979) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5457493 + ... + 5457496.

Almost surely, 2^21829978 is an apocalyptic number.

21829978 is a deficient number, since it is larger than the sum of its proper divisors (10914992).

21829978 is a wasteful number, since it uses less digits than its factorization.

21829978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10914991.

The product of its digits is 145152, while the sum is 46.

The square root of 21829978 is about 4672.2562001671. The cubic root of 21829978 is about 279.4802347340.

It can be divided in two parts, 2182997 and 8, that added together give a triangular number (2183005 = T₂₀₈₉).

The spelling of 21829978 in words is "twenty-one million, eight hundred twenty-nine thousand, nine hundred seventy-eight".