A227980 Numbers n such that sigma(n-1) - sigma(n+1) >= sigma(n); where sigma(n) = A000203(n) = sum of the divisors of n.

61, 73, 121, 145, 181, 193, 217, 241, 253, 301, 313, 337, 361, 397, 421, 433, 457, 481, 505, 541, 577, 601, 613, 625, 631, 661, 673, 721, 757, 781, 793, 817, 841, 865, 901, 913, 925, 937, 961, 1009, 1021, 1051, 1057, 1081, 1093, 1141, 1153, 1171, 1177, 1201

Offset

1,1

Comments

There is no number n < 100000 such that sigma(n-1) - sigma(n+1) = sigma(n).

Complement of A227981.

Links

Jaroslav Krizek, Table of n, a(n) for n = 1..2000

Example

Number  61 is in the sequence because sigma(60) - sigma(62) = 168 - 96 = 72 > sigma(61) = 62.

Mathematica

Flatten[Position[Partition[DivisorSigma[1, Range[1300]], 3, 1], _?(#[[1]]-#[[3]]>=#[[2]]&), 1, Heads->False]]+1 (* Harvey P. Dale, Jan 20 2025 *)

Crossrefs

Cf. A000203, A227981.

Sequence in context: A109549 A139944 A179012 * A364662 A227520 A033236

Adjacent sequences: A227977 A227978 A227979 * A227981 A227982 A227983

Keyword

nonn

Author

Jaroslav Krizek, Aug 02 2013

Status

approved