21247640 has 32 divisors (see below), whose sum is σ = 48001680. Its totient is φ = 8464512.

The previous prime is 21247631. The next prime is 21247649. The reversal of 21247640 is 4674212.

It is an interprime number because it is at equal distance from previous prime (21247631) and next prime (21247649).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21247649) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10382 + ... + 12258.

Almost surely, 2^21247640 is an apocalyptic number.

21247640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21247640 is an abundant number, since it is smaller than the sum of its proper divisors (26754040).

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

21247640 is a wasteful number, since it uses less digits than its factorization.

21247640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2171 (or 2167 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 26.

The square root of 21247640 is about 4609.5162435987. The cubic root of 21247640 is about 276.9726586593.

The spelling of 21247640 in words is "twenty-one million, two hundred forty-seven thousand, six hundred forty".