

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
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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



KEYWORD

nonn


AUTHOR



STATUS

approved



