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A316100 Numbers k such that k is deficient but k+1 is abundant, that is, a deficient number followed by an abundant number. 0
11, 17, 19, 23, 29, 35, 39, 41, 47, 53, 55, 59, 65, 69, 71, 77, 79, 83, 87, 89, 95, 99, 101, 103, 107, 111, 113, 119, 125, 131, 137, 139, 143, 149, 155, 159, 161, 167, 173, 175, 179, 185, 191, 195, 197, 199, 203, 207, 209, 215, 219, 221, 223, 227, 233, 239 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
11 is deficient and 12 is abundant.
17 is deficient and 18 is abundant.
MAPLE
with(numtheory): select(n->sigma(n)<2*n and sigma(n+1)>2*(n+1), [$1..400]);
MATHEMATICA
Select[Range@ 240, And[DivisorSigma[1, #] < 2 #, DivisorSigma[1, # + 1] > 2 (# + 1)] &] (* Michael De Vlieger, Jul 01 2018 *)
PROG
(GAP) Filtered([1..400], n->Sigma(n)<2*n and Sigma(n+1)>2*(n+1));
(PARI) isok(n) = (sigma(n) < 2*n) && (sigma(n+1) > 2*(n+1)); \\ Michel Marcus, Jul 02 2018
CROSSREFS
Sequence in context: A217063 A038966 A050778 * A049593 A216664 A019412
KEYWORD
nonn
AUTHOR
Muniru A Asiru, Jul 01 2018
STATUS
approved

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Last modified May 21 02:29 EDT 2024. Contains 372720 sequences. (Running on oeis4.)