login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A108750 Even numbers n such that there exists a solution to lcm(r+s,t) = n-1, lcm(s,r+t) = n-2, r,s>0, t>1, r+s+t <= n. 0
58, 146, 156, 206, 288, 466, 478, 496, 498, 562, 596, 610, 640, 716, 738, 782, 834, 838, 870, 982, 1028, 1068, 1162, 1234, 1276, 1314, 1336, 1366, 1636, 1706, 1718, 1856, 1888, 1982, 2110, 2148, 2186, 2206, 2228, 2416, 2452, 2612, 2626, 2642, 2666, 2668 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The alternating groups A_n with n even can be generated by a 3-cycle x=(1,2,3) and an (n-1)-cycle y=(2,3,...n) whose product has cycle type 2 x (n-2). These are called standard generators of A_n. If we assume only that o(y)=n-1 and o(xy)=n-2, then for the values of n in the sequence, y could be the product of 2 cycles (cycle type (r+s).t) and xy can have cycle type s.(r+t). Thus the elements of the sequence give those alternating groups A_n which contain pairs of elements which look like standard generators if one only looks at their orders.

LINKS

Table of n, a(n) for n=1..46.

EXAMPLE

a(1)=58 because we can take r=11, s=8, t=3 giving lcm(19,3)=57, lcm(8,14)=56

MATHEMATICA

maxTerm = 3000; f[n_] := Module[{cond = False}, Do[r = rs-s; If[r == rt-t && r > 0 && r+s+t <= n, If[LCM[r+s, t] == n-1 && LCM[s, r+t] == n-2, cond = True; Break[]]], {t, Rest[Divisors[n-1]]}, {s, Divisors[n-2]}, {rs, Divisors[n-1]}, {rt, Divisors[n-2]}]; cond]; Reap[For[n = 0; k = 2, k <= maxTerm, k = k+2, If[f[k], n++; Print["a(", n, ") = ", k]; Sow[k]]]][[2, 1]] (* Jean-Fran├žois Alcover, May 06 2017 *)

CROSSREFS

Cf. A108157.

Sequence in context: A118153 A225788 A250733 * A044390 A044771 A127025

Adjacent sequences:  A108747 A108748 A108749 * A108751 A108752 A108753

KEYWORD

nonn

AUTHOR

Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jun 23 2005

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 29 23:00 EDT 2022. Contains 354913 sequences. (Running on oeis4.)