The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A247473 Numbers of the form 2^k (k>=0) that are a sum of divisors of n for some n. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 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. LINKS FORMULA a(1) = 1, for n>=2, a(n) = 2^A180221(n-1). EXAMPLE 32 = 2^5 is in sequence because there are numbers n = 21 and 31 with sigma(n) = 32. PROG (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)]] CROSSREFS Cf. A000079, A000203, A046528, A078426, A094502, A094505, A180221. Sequence in context: A068205 A241684 A254878 * A113479 A252540 A327493 Adjacent sequences:  A247470 A247471 A247472 * A247474 A247475 A247476 KEYWORD nonn AUTHOR Jaroslav Krizek, Feb 27 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 7 12:19 EDT 2020. Contains 336276 sequences. (Running on oeis4.)