661621 has 2 divisors, whose sum is σ = 661622. Its totient is φ = 661620.

The previous prime is 661613. The next prime is 661663. The reversal of 661621 is 126166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 422500 + 239121 = 650^2 + 489^2 .

It is a cyclic number.

It is not a de Polignac number, because 661621 - 2³ = 661613 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 661592 and 661601.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330810 + 330811.

It is an arithmetic number, because the mean of its divisors is an integer number (330811).

2⁶⁶¹⁶²¹ is an apocalyptic number.

It is an amenable number.

661621 is a deficient number, since it is larger than the sum of its proper divisors (1).

661621 is an equidigital number, since it uses as much as digits as its factorization.

661621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 432, while the sum is 22.

The square root of 661621 is about 813.4008851729. The cubic root of 661621 is about 87.1370983256.

Adding to 661621 its reverse (126166), we get a palindrome (787787).

The spelling of 661621 in words is "six hundred sixty-one thousand, six hundred twenty-one".