21122

Appears in sequences

• Replace n with concatenation of its divisors >1.at n=21A037277
• Numbers k such that 297*2^k-1 is prime.at n=41A050907
• Consider the version of the Collatz or 3x+1 problem where x -> x/2 if x is even, x -> (3x+1)/2 if x is odd. Define the stopping time of x to be the number of steps needed to reach 1. Sequence gives the number of integers x with stopping time n.at n=36A060322
• Numbers with digits 1 and 2 and at least one of each.at n=40A111066
• Expansion of (-2+3*x+3*x^2+4*x^3+3*x^4-5*x^5)/((x-1)*(x+1)*(1+x^2)*(x^2-3*x+1)).at n=12A111666
• Numbers k such that the number of divisors of k equals both the sum and the product of digits of k in base 10.at n=5A113761
• Number of permutations of length n which avoid the patterns 2314, 3241, 4312.at n=9A116784
• Numbers n such that sigma(n) and sigma(sigma(n)) are both perfect squares.at n=26A134263
• Numbers n with property that for each single digit d of the base 3 expansion of n, we can also see the base 3 expansion of d^2 as a substring. Also n may not contain any 0 digits.at n=27A135464
• First differences of A175111.at n=4A175112
• Row sums of A186430.at n=9A186431
• Numbers 3*n + 2 written in base 3.at n=68A190642
• Triangle read by rows in which row n lists the binary words of length n over the alphabet {1,2} with no initial repeats.at n=23A211029
• List of primitive words over the alphabet {1,2}.at n=40A213969
• List of subwords (or factors) of the Thue-Morse "1,2"-word A001285.at n=29A214215
• Minimal representation (considered minimal in any canonical base b >= 3) of n in a binary system using two distinct digits "1" and "2", not allowing zeros, where a digit d in position p (p = 1,2,3,...,n) represents the value d^p.at n=39A235860
• Number of magic labelings of the prism graph I X C_7 with magic sum n.at n=5A244873
• Number of nX4 0..1 arrays with every element equal to 0, 1, 4 or 5 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero.at n=14A302511
• If pd(x) is the product of the digits of the number x and sd(x) the sum of the digits of the number x then the sequence lists all the positive numbers n for which pd(n) = sd(n) and sd(pd(n)) = pd(sd(n)).at n=38A305257
• The Wythoff representation of n: an alternative way of presenting A189921.at n=31A317208