OFFSET
1,1
COMMENTS
Jensen and Bussian suggested the calculation of this sequence as a part of a student research project.
LINKS
David W. Jensen and Michael K. Keane, A Number-Theoretic Approach to Subgroups of Dihedral Groups, USAFA-TR-90-2, Air Force Academy Colorado Springs, Colorado, 1990.
David W. Jensen and Eric R. Bussian, A Number-Theoretic Approach to Counting Subgroups of Dihedral Groups, The College Mathematics Journal, Vol. 23, No. 2 (1992), pp. 150-152.
EXAMPLE
144 is in the sequence since (144, 274) is a pair of dihedral amicable numbers: sigma(144) + d(144) = 403 + 15 = 418, sigma(274) + d(274) = 414 + 4 = 418, and 144 + 274 = 418.
MATHEMATICA
t[n_] := DivisorSigma[0, n] + DivisorSigma[1, n] - n; s={}; Do[n = t[m]; If[n>m && t[n]==m, AppendTo[s, m]], {m, 1, 100000}]; s
PROG
(PARI) f(n) = numdiv(n) + sigma(n) - n;
isok(n) = my(nn = f(n)); (nn > n) && (n == f(nn)); \\ Michel Marcus, Dec 04 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Dec 01 2018
STATUS
approved