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!)
A257591 Odd numbers which are not prime powers but which have a proper divisor == 1 mod 4. 4

%I #17 Jun 19 2015 04:58:17

%S 15,35,39,45,51,55,63,65,75,85,87,91,95,99,105,111,115,117,119,123,

%T 135,143,145,147,153,155,159,165,171,175,183,185,187,189,195,203,205,

%U 207,215,219,221,225,231,235,245,247,255,259,261,265,267,273,275,279,285

%N Odd numbers which are not prime powers but which have a proper divisor == 1 mod 4.

%H Hiroaki Yamanouchi, <a href="/A257591/b257591.txt">Table of n, a(n) for n = 1..3124</a>

%H R. Lauterbach, <a href="http://dx.doi.org/10.1007/s10884-014-9402-1">Equivariant Bifurcation and Absolute Irreducibility in R^8: A Contribution to Ize Conjecture and Related Bifurcations</a>, Journal of Dynamics and Differential Equations, Oct 2014; DOI 10.1007/s10884-014-9402-1.

%e 63 = 7*9 is not a power of a prime and has a proper divisor 9 == 1 mod 4.

%o (PARI) lista(nn) = {forstep(n=1, nn, 2, if (!isprimepower(n) && sumdiv(n, d, (d != 1) && (d != n) && ((d % 4)==1)), print1(n, ", ")););} \\ _Michel Marcus_, Jun 19 2015

%Y Subsequence of A061346.

%K nonn

%O 1,1

%A _N. J. A. Sloane_, May 14 2015

%E a(7)=57 removed and a(11)-a(55) added by _Hiroaki Yamanouchi_, May 20 2015

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 March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)