Number of the day: 649

János Bolyai was born on this day 218 years ago.

Properties of the number 649:

649 is a cyclic number.
649 = 11 × 59 is semiprime and squarefree.
649 has 2 distinct prime factors, 4 divisors, 5 antidivisors and 580 totatives.
649 has a prime digit sum 19 in base 10.
Reversing the decimal digits of 649 results in a sphenic number.
Reversing the decimal digits of 649 results in a triangular number.
649 = 2² + … + 12² is the sum of at least 2 consecutive positive squares in 1 way.
649 = 325² - 324² = 35² - 24² is the difference of 2 nonnegative squares in 2 ways.
649 is the sum of 2 positive triangular numbers.
649 is the difference of 2 positive pentagonal numbers in 1 way.
649 = 3² + 8² + 24² is the sum of 3 positive squares.
649² is the sum of 3 positive squares.
649 is a proper divisor of 353² - 1.
649 = '6' + '49' is the concatenation of 2 semiprime numbers.
649 is an emirpimes in (at least) the following bases: 2, 4, 6, 7, 11, 16, 18, 19, 20, 23, 25, 26, 27, 29, 30, 33, 34, 42, 43, 44, 45, 47, 50, 63, 64, 65, 66, 67, 69, 70, 74, 75, 79, 82, 84, 87, 88, 89, 90, 91, and 97.
649 is palindromic in (at least) the following bases: 24, 58, -8, -17, -27, -36, -54, -72, and -81.
649 in base 8 = 1211 and consists of only the digits '1' and '2'.
649 in base 23 = 155 and consists of only the digits '1' and '5'.
649 in base 24 = 131 and consists of only the digits '1' and '3'.

The number 649 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A000960: Flavius Josephus's sieve: Start with the natural numbers; at the k-th sieving step, remove every (k+1)-st term of the sequence remaining after the (k-1)-st sieving step; iterate.
A003355: Numbers that are the sum of 10 positive 5th powers.
A024206: Expansion of x^2*(1+x-x^2)/((1-x^2)*(1-x)^2).
A028387: a(n) = n + (n+1)^2.
A051424: Number of partitions of n into pairwise relatively prime parts.
A058331: a(n) = 2*n^2 + 1.
A078972: Brilliant numbers: semiprimes (products of two primes, A001358) whose prime factors have the same number of decimal digits.
A166459: Numbers whose sum of digits is 19.
A195162: Generalized 12-gonal numbers: k*(5*k-4) for k = 0, +-1, +-2, ...
A333218: Numbers k such that the k-th composition in standard order is a permutation (of an initial interval).