A247473 Numbers of the form 2^k (k>=0) that are a sum of divisors of n for some n.

1, 4, 8, 32, 128, 256, 512, 1024, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648, 4294967296, 8589934592, 17179869184, 34359738368

Offset: 1

Author

Jaroslav Krizek, Feb 27 2015

Keywords

• nonn

Comments

Set of values A094502(n) = sigma(A046528(n)) in increasing order.

Complement of A094505 with respect to A000079 (powers of 2).

Corresponding values of numbers k>0 are in A180221.

Examples

			32 = 2^5 is in sequence because there are numbers n = 21 and 31 with sigma(n) = 32.
		

Crossrefs

Cf. A000079, A000203, A046528, A078426, A094502, A094505, A180221.

Programs

Magma

Set(Sort([SumOfDivisors(n): n in [A046528(n)]]))

Magma

Set(Sort([SumOfDivisors(n): n in[1..10000], k in [0..100] | SumOfDivisors(n) eq 2^k]))

Magma

[1] cat [2^n: n in[A180221(n)]]

Formula

a(1) = 1, for n>=2, a(n) = 2^A180221(n-1).