21009456 has 200 divisors, whose sum is σ = 69318480. Its totient is φ = 6096384.

The previous prime is 21009449. The next prime is 21009491. The reversal of 21009456 is 65490012.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 488571 + ... + 488613.

Almost surely, 2^21009456 is an apocalyptic number.

21009456 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21009456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34659240).

21009456 is an abundant number, since it is smaller than the sum of its proper divisors (48309024).

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

21009456 is a wasteful number, since it uses less digits than its factorization.

21009456 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105 (or 90 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21009456 is about 4583.6073130232. The cubic root of 21009456 is about 275.9338215623.

21009456 divided by its sum of digits (27) gives a triangular number (778128 = T₁₂₄₇).

Adding to 21009456 its reverse (65490012), we get a palindrome (86499468).

The spelling of 21009456 in words is "twenty-one million, nine thousand, four hundred fifty-six".