A325380 - OEIS

%I #10 Jun 18 2019 07:24:18

%S 801,1377,1773,2525,3725,4689,4753,6309,6425,7209,7677,8577,8957,9477,

%T 11133,11225,11493,11925,12393,12429,12789,13077,15381,15777,18873,

%U 19269,19845,20025,20629,21213,24201,26073,26721,28037,28989,29277,29961,30037,30213,31925,32553,33273,34425,34677,36369,36441,38725,39249,40329

%N Numbers k in A228058 such that also A001065(k) is in A228058.

%C If any odd perfect number exists, then it must occur in this sequence.

%H Antti Karttunen, <a href="/A325380/b325380.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/O#opnseqs">Index entries for sequences where any odd perfect numbers must occur</a>

%o (PARI)

%o A001065(n) = (sigma(n)-n);

%o isA228058(n) = if(!(n%2)||(omega(n)<2),0,my(f=factor(n),y=0); for(i=1,#f~,if(1==(f[i,2]%4), if((1==y)||(1!=(f[i,1]%4)),return(0),y=1), if(f[i,2]%2, return(0)))); (y));

%o k=0; n=0; while(k<100,n++; if(isA228058(n)&&isA228058(A001065(n)), k++; print1(n,", ")));

%Y Cf. A001065, A228058, A325377.

%K nonn

%O 1,1

%A _Antti Karttunen_, Apr 22 2019