OFFSET
1,1
COMMENTS
3*10^11 < a(13) <= 1245273287760. a(14) = 72462882816. - Donovan Johnson, Dec 25 2011
EXAMPLE
8 and 10 have 4 divisors each, 7 and 11 have 2 divisors each, but 6 and 12 have different numbers of divisors; thus 9 has divisor symmetry 2. Since no smaller number has this, a(2) = 9.
PROG
(PARI) a(n)=my(k=n); while(k++, for(i=1, n, if(numdiv(k-i)!=numdiv(k+i), next(2))); if(numdiv(k-n-1)==numdiv(k+n+1), next); return(k))
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Charles R Greathouse IV, Dec 19 2011
EXTENSIONS
a(11) from Donovan Johnson, Dec 20 2011
a(12) from Donovan Johnson, Dec 25 2011
STATUS
approved