21279690 has 48 divisors (see below), whose sum is σ = 55898856. Its totient is φ = 5616000.

The previous prime is 21279689. The next prime is 21279691. The reversal of 21279690 is 9697212.

It is an interprime number because it is at equal distance from previous prime (21279689) and next prime (21279691).

It can be written as a sum of positive squares in 4 ways, for example, as 21095649 + 184041 = 4593^2 + 429^2 .

It is a super-2 number, since 2×21279690² = 905650412992200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21279691) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7920 + ... + 10260.

Almost surely, 2^21279690 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21279690, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27949428).

21279690 is an abundant number, since it is smaller than the sum of its proper divisors (34619166).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21279690 is a wasteful number, since it uses less digits than its factorization.

21279690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2455 (or 2452 counting only the distinct ones).

The product of its (nonzero) digits is 13608, while the sum is 36.

The square root of 21279690 is about 4612.9914372346. The cubic root of 21279690 is about 277.1118508095. Note that the first 3 decimals are identical.

The spelling of 21279690 in words is "twenty-one million, two hundred seventy-nine thousand, six hundred ninety".