A227983 Numbers n such that sigma(n+1) - sigma(n-1) < sigma(n); where sigma(n) = A000203(n) = sum of the divisors of n.
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73
Offset: 1
Keywords
Examples
Number 60 is in the sequence because sigma(61) - sigma(59) = 62 - 60 = 2 < sigma(60) = 168.
Links
- Jaroslav Krizek, Table of n, a(n) for n = 1..2000
Programs
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Mathematica
Flatten[Position[Partition[DivisorSigma[1,Range[100]],3,1],?(#[[3]]- #[[1]]< #[[2]]&),1,Heads->False]]+1 (* _Harvey P. Dale, Jul 25 2021 *)
Comments