21621437 has 2 divisors, whose sum is σ = 21621438. Its totient is φ = 21621436.

The previous prime is 21621427. The next prime is 21621463. The reversal of 21621437 is 73412612.

It is an a-pointer prime, because the next prime (21621463) can be obtained adding 21621437 to its sum of digits (26).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14830201 + 6791236 = 3851^2 + 2606^2 .

It is a cyclic number.

It is not a de Polignac number, because 21621437 - 2⁴ = 21621421 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21621427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810718 + 10810719.

It is an arithmetic number, because the mean of its divisors is an integer number (10810719).

Almost surely, 2^21621437 is an apocalyptic number.

It is an amenable number.

21621437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621437 is an equidigital number, since it uses as much as digits as its factorization.

21621437 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 26.

The square root of 21621437 is about 4649.8856975199. The cubic root of 21621437 is about 278.5874307955.

The spelling of 21621437 in words is "twenty-one million, six hundred twenty-one thousand, four hundred thirty-seven".