21023661 has 8 divisors (see below), whose sum is σ = 28057984. Its totient is φ = 14002560.

The previous prime is 21023641. The next prime is 21023663. The reversal of 21023661 is 16632012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21023661 - 2⁷ = 21023533 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21023663) 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, 1341 + ... + 6621.

It is an arithmetic number, because the mean of its divisors is an integer number (3507248).

Almost surely, 2^21023661 is an apocalyptic number.

It is an amenable number.

21023661 is a deficient number, since it is larger than the sum of its proper divisors (7034323).

21023661 is a wasteful number, since it uses less digits than its factorization.

21023661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6611.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21023661 is about 4585.1565949267. The cubic root of 21023661 is about 275.9959960562.

Adding to 21023661 its reverse (16632012), we get a palindrome (37655673).

It can be divided in two parts, 210 and 23661, that added together give a triangular number (23871 = T₂₁₈).

The spelling of 21023661 in words is "twenty-one million, twenty-three thousand, six hundred sixty-one".