OFFSET
1,1
COMMENTS
REFERENCES
J.-M. De Koninck & A. Mercier, 1001 Problèmes en Théorie Classique des Nombres, Problème 620 pp. 82, 280, Ellipses Paris 2004
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
sigma(77) = 1+7+11+77 = 96 < sigma(76) = 1+2+4+19+38+76 = 140, hence composite 77 is a term.
sigma(135) = 1+3+5+9+15+27+45+135 = 240 > sigma(134) = 1+2+67+134 = 204, hence composite 135 is not a term.
MAPLE
filter:= m -> not isprime(m) and numtheory:-sigma(m) < numtheory:-sigma(m-1) : select(filter, [$1..500]);
MATHEMATICA
Select[Range[200], CompositeQ[#] && DivisorSigma[1, #] < DivisorSigma[1, # - 1] &] (* Amiram Eldar, Mar 12 2020 *)
PROG
(PARI) isok(m) = (m>1) && !isprime(m) && (sigma(m) < sigma(m-1)); \\ Michel Marcus, Mar 15 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Bernard Schott, Mar 12 2020
STATUS
approved