login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

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 *)

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

Cf. A005100, A005101.

Sequence in context: A217063 A038966 A050778 * A049593 A216664 A019412

Adjacent sequences:  A316097 A316098 A316099 * A316101 A316102 A316103

KEYWORD

nonn

AUTHOR

Muniru A Asiru, Jul 01 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 30 04:45 EDT 2021. Contains 346348 sequences. (Running on oeis4.)