OFFSET
1,1
COMMENTS
It appears that most of the terms are divisible by 3; the smallest exception is 13475.
Up to 10^9, 223182 of 20606497 (about 1%) of the terms are not divisible by 3. - Charles R Greathouse IV, Nov 28 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
sigma(62) = 96, sigma(63) = 104, sigma(64) = 127. Hence, 63 is in the sequence.
sigma(74) = 114, sigma(75) = 124, sigma(76) = 140. Hence, 75 is in the sequence.
MAPLE
Sigmas:= map(numtheory:-sigma, [$1..3000]):
select(t -> Sigmas[t-1] < Sigmas[t] and Sigmas[t] < Sigmas[t+1],
[seq(i, i=3..3000, 2)]); # Robert Israel, Nov 23 2019
MATHEMATICA
Select[Range[1, 8000, 2], DivisorSigma[1, # - 1] < DivisorSigma[1, (#)] && DivisorSigma[1, #] < DivisorSigma[1, (# + 1)] &]
PROG
(Magma) f:=func<n| DivisorSigma(1, n) lt DivisorSigma(1, n+1) >; [k:k in [3..2500 by 2]| f(k-1) and f(k)] // Marius A. Burtea, Nov 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Nov 19 2019
STATUS
approved