OFFSET
1,1
COMMENTS
Does this sequence have finite density? - Franklin T. Adams-Watters, Jun 18 2009
See A300869 for the odd terms, much less frequent since they can only occur for x = k^2 or 2*k^2. - M. F. Hasler, Mar 16 2018
LINKS
Franklin T. Adams-Watters, Table of n, a(n) for n = 1..1095 (terms <= 10000)
EXAMPLE
a(1)=12 as the multiplicity of the value 12 is 2: 12 = sigma(6) = sigma(11).
PROG
(PARI)
na(n) = local(v, s); v=vector(n); for(k=1, n, s=sigma(k); if(s<=n, v[s]++)); v
la(n) = local(v, r); v=na(n); r=[]; for(k=1, n, if(v[k]>1, r=concat(r, [k]))); r \\ Franklin T. Adams-Watters, Jun 18 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Apr 25 2009
EXTENSIONS
Edited and extended by R. J. Mathar, Apr 28 2009
STATUS
approved