21472309 has 4 divisors (see below), whose sum is σ = 22735404. Its totient is φ = 20209216.

The previous prime is 21472291. The next prime is 21472313. The reversal of 21472309 is 90327412.

21472309 = T₃₇₈₂ + T₃₇₈₃ + T₃₇₈₄.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10562500 + 10909809 = 3250^2 + 3303^2 .

It is a cyclic number.

It is not a de Polignac number, because 21472309 - 2⁵ = 21472277 is a prime.

It is a super-2 number, since 2×21472309² = 922120107582962, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21472379) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 631522 + ... + 631555.

It is an arithmetic number, because the mean of its divisors is an integer number (5683851).

Almost surely, 2^21472309 is an apocalyptic number.

21472309 is the 3784-th centered triangular number.

It is an amenable number.

21472309 is a deficient number, since it is larger than the sum of its proper divisors (1263095).

21472309 is a wasteful number, since it uses less digits than its factorization.

21472309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1263094.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 21472309 is about 4633.8222883490. The cubic root of 21472309 is about 277.9454588239.

The spelling of 21472309 in words is "twenty-one million, four hundred seventy-two thousand, three hundred nine".