21457661 has 8 divisors (see below), whose sum is σ = 21832440. Its totient is φ = 21086208.

The previous prime is 21457649. The next prime is 21457679. The reversal of 21457661 is 16675412.

21457661 is nontrivially palindromic in base 13.

It can be written as a sum of positive squares in 4 ways, for example, as 122500 + 21335161 = 350^2 + 4619^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21457661 - 2²² = 17263357 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 (21450661) 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, 14525 + ... + 15933.

It is an arithmetic number, because the mean of its divisors is an integer number (2729055).

Almost surely, 2^21457661 is an apocalyptic number.

It is an amenable number.

21457661 is a deficient number, since it is larger than the sum of its proper divisors (374779).

21457661 is a wasteful number, since it uses less digits than its factorization.

21457661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1663.

The product of its digits is 10080, while the sum is 32.

The square root of 21457661 is about 4632.2414660723. The cubic root of 21457661 is about 277.8822414147.

It can be divided in two parts, 214 and 57661, that added together give a palindrome (57875).

The spelling of 21457661 in words is "twenty-one million, four hundred fifty-seven thousand, six hundred sixty-one".