OFFSET
1,1
COMMENTS
Strict local minimums of sigma(n) of the 2nd order:
sigma(n) is less than any of 4 closest neighbors.
b(n) = the first term ending with n=1..9:
11,22683662,23,17254,635,69686,17,6143138,29
c(n) = position of b(n) in the sequence:
1,3781722,3,2872,105,11608,2,1024132,4.
The term in the sequence ending with zero should be very large (>~10^80 according to Charles R Greathouse IV).
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MATHEMATICA
sminQ[{a_, b_, c_, d_, e_}]:=c<Min[{a, b, d, e}]; Flatten[ Position[ Partition[ DivisorSigma[ 1, Range[400]], 5, 1], _?sminQ]]+2 (* Harvey P. Dale, Aug 12 2014 *)
PROG
(PARI) {for(n=3, 10^10, sigma(n)<vecmin([sigma(n-2), sigma(n-1),
sigma(n+1), sigma(n+2)])&print(n, ", "))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Oct 08 2010
STATUS
approved