A316100 - OEIS

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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.

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

Table of n, a(n) for n=1..56.

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 *)