21045

Appears in sequences

• Numbers n such that sigma(n+1)-sigma(n) = -sigma(n)/d(n), where d(n) denotes the number of divisors of n.at n=7A066177
• a(n) = 3*a(n-1) + a(n-2) + n.at n=8A117917
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 1), (0, 1, -1), (0, 1, 1), (1, 0, 0), (1, 0, 1)}.at n=7A151141
• a(n)=n+floor(r*a(n-1)), where r = golden ratio = (1+sqrt(5))/2, a(0)=0, a(1)=1.at n=18A182640
• E.g.f.: exp( Sum_{n>=1} n!*x^(2*n)/(2*n)! ) = Sum_{n>=0} a(n)*x^(2*n)/(2*n)!.at n=5A193444
• Composite squarefree numbers k such that the arithmetic mean of the distinct prime factors of k is a prime p, and p divides k.at n=34A229094
• Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 569", based on the 5-celled von Neumann neighborhood.at n=26A272993
• Analog of A265434 that counts only primitive words.at n=23A276408
• Position of start of first occurrence of palindromic prime(n) after the decimal point in expansion of Pi.at n=40A309343
• Heinz numbers of integer partitions whose reciprocal sum is 1.at n=16A316855
• Heinz numbers of aperiodic integer partitions into relatively prime parts whose reciprocal sum is 1.at n=8A316888
• Heinz numbers of aperiodic integer partitions whose reciprocal sum is 1.at n=12A316889
• Heinz numbers of integer partitions into relatively prime parts whose reciprocal sum is 1.at n=8A316890
• Heinz numbers of integer partitions into relatively prime parts whose reciprocal sum is the reciprocal of an integer.at n=13A316901
• Number of n element multisets of the 15th roots of unity with zero sum.at n=48A321418