A292763 - OEIS

%I #17 Oct 09 2017 15:29:32

%S 1,3,5,6,7,10,11,13,14,17,19,20,22,23,26,27,29,31,34,37,38,40,41,43,

%T 45,46,47,52,53,54,58,59,61,62,67,68,71,73,74,79,80,82,83,86,89,90,94,

%U 97,101,103,104,106,107,109,113,116,117,118,122,127,131,134,136,137,139,142,146,148,149,151,153,157

%N Numbers m such that sigma(m)+phi(m) == 2 mod 4.

%C Union of {1}, A191217 and A292762.

%H Vincenzo Librandi, <a href="/A292763/b292763.txt">Table of n, a(n) for n = 1..5000</a>

%H N. J. A. Sloane, Three (No, 8) Lovely Problems from the OEIS, Experimental Mathematics Seminar, Rutgers University, Oct 05 2017, <a href="https://vimeo.com/237029685">Part I</a>, <a href="https://vimeo.com/237030304">Part 2</a>, <a href="https://oeis.org/A290447/a290447_slides.pdf">Slides.</a> (Mentions this sequence)

%t Do[If[Mod[DivisorSigma[1, n] + EulerPhi[n], 4]==2, Print[n]], {n, 1, 10^3}] (* _Vincenzo Librandi_, Oct 02 2017 *)

%o (PARI) isok(m) = ((sigma(m)+eulerphi(m)) % 4) == 2; \\ _Michel Marcus_, Oct 02 2017

%Y Cf. A000010, A000203.

%Y Cf. A191217, A292762.

%Y A065091 (odd primes) is a subsequence. - _Michel Marcus_, Oct 02 2017

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Sep 26 2017