21951639 has 6 divisors (see below), whose sum is σ = 31707936. Its totient is φ = 14634420.

The previous prime is 21951623. The next prime is 21951653. The reversal of 21951639 is 93615912.

21951639 is a `hidden beast` number, since 2 + 19 + 5 + 1 + 639 = 666.

It is not a de Polignac number, because 21951639 - 2⁴ = 21951623 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21951739) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1219527 + ... + 1219544.

It is an arithmetic number, because the mean of its divisors is an integer number (5284656).

Almost surely, 2^21951639 is an apocalyptic number.

21951639 is a deficient number, since it is larger than the sum of its proper divisors (9756297).

21951639 is a wasteful number, since it uses less digits than its factorization.

21951639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2439077 (or 2439074 counting only the distinct ones).

The product of its digits is 14580, while the sum is 36.

The square root of 21951639 is about 4685.2576236532. The cubic root of 21951639 is about 279.9984651276.

The spelling of 21951639 in words is "twenty-one million, nine hundred fifty-one thousand, six hundred thirty-nine".