This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A124144 Perfect powers pp such that sigma(n)=pp for some abundant number n. 0

%I

%S 144,216,576,784,961,1296,1728,1764,2304,2744,3136,3600,3844,4356,

%T 5184,6084,7056,7776,8100,9216,11664,12544,13824,14400,15376,15876,

%U 17424,19600,20736,21952,24336,28224

%N Perfect powers pp such that sigma(n)=pp for some abundant number n.

%e a(1)=144 since sigma(66)=144>2*66=132.

%p with(numtheory); egcd := proc(n::posint) local L; if n>1 then L:=ifactors(n)[2]; L:=map(z->z[2],L); return igcd(op(L)) else return 1 fi; end; L:=[]: P:={}: for w to 1 do for n from 1 to 10000 do s:=sigma(n); if s>2*n and egcd(s)>1 then print(n,s,ifactor(s)); L:=[op(L),n]; P:=P union {s}; fi od od; L; P;

%Y Cf. A001597, A005101, A065496.

%K nonn

%O 1,1

%A _Walter Kehowski_, Dec 01 2006

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.

Last modified December 14 17:44 EST 2019. Contains 329979 sequences. (Running on oeis4.)