A109788 Admirable numbers whose abundance is < 10.

12, 20, 56, 70, 88, 104, 368, 464, 650, 836, 1888, 1952, 4030, 5830, 8925, 11096, 17816, 32128, 32445, 45356, 77744, 91388, 128768, 130304, 254012, 388076, 442365, 521728, 522752, 1848964, 2087936, 2291936, 8378368, 8382464, 13174976, 29465852, 35021696, 45335936

Offset

1,1

Comments

Apparently all the abundant numbers with even abundance < 10 are admirable (checked for the first 60 terms). Of the 4 known numbers whose abundance is 10 (A223609), only the first, 40, is admirable. - Amiram Eldar, Nov 07 2019

Links

Amiram Eldar, Table of n, a(n) for n = 1..60

Mathematica

aQ[n_] := (ab = DivisorSigma[1, n] - 2 n) > 0 && EvenQ[ab] && ab < 10 && ab/2 < n && Divisible[n, ab/2]; Select[Range[10^4], aQ] (* Amiram Eldar, Nov 07 2019 *)

Prog

(PARI) for(n=1, 10^9, ap=sigma(n)-2*n; if(ap>0 && ap<10 && (ap%2)==0, d=ap/2; if(d!=n && (n%d)==0, print1(n", ")))) - Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008

Crossrefs

Cf. A033880, A111592, A111667.

Sequence in context: A063690 A229355 A259174 * A341361 A181701 A025104

Adjacent sequences: A109785 A109786 A109787 * A109789 A109790 A109791

Keyword

nonn

Author

Jason Earls, Aug 14 2005

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008

a(36)-a(38) from Amiram Eldar, Nov 07 2019

Status

approved