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A053248 Second differences of sigma(n) that are negative. 2
1, 4, 10, 9, 11, 30, 10, 20, 40, 32, 16, 65, 13, 42, 82, 46, 12, 96, 26, 82, 106, 46, 18, 143, 57, 70, 114, 88, 40, 214, 26, 66, 136, 88, 120, 244, 30, 60, 160, 171, 47, 256, 36, 150, 266, 96, 40, 286, 88, 176, 226, 124, 12, 24, 342, 170, 230, 222, 94, 34, 443, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = A053223(A053229(n)).
MAPLE
with (numtheory): f := [seq( sigma(i+2) - sigma(i+1) - (sigma(i+1) - sigma(i)), i=1..200)];
seq(`if`(f[i] < 0, f[i], print( )), i=1..200);
MATHEMATICA
Abs[Select[Differences[DivisorSigma[1, Range[200]], 2], Negative]] (* Harvey P. Dale, Aug 13 2015 *)
CROSSREFS
Sequence in context: A073722 A320577 A199805 * A081547 A264272 A264257
KEYWORD
nonn
AUTHOR
Asher Auel, Jan 11 2000
STATUS
approved

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Last modified May 24 05:24 EDT 2024. Contains 372772 sequences. (Running on oeis4.)