OFFSET
1,2
COMMENTS
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
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Feb 27 2015
STATUS
approved