This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A296213 a(n) = 1 if both 1+phi(k) and 1+sigma(k) are squares, 0 otherwise. 2

%I

%S 0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

%T 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,

%U 0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1

%N a(n) = 1 if both 1+phi(k) and 1+sigma(k) are squares, 0 otherwise.

%C Characteristic function of A063532, numbers k such that phi(k) + 1 = x^2 and sigma(k) + 1 = y^2 for some x and y.

%H Antti Karttunen, <a href="/A296213/b296213.txt">Table of n, a(n) for n = 1..65593</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%e a(15) = 1 because both 1+phi(15) = 9 and 1+sigma(15) = 25 are squares.

%t Table[If[AllTrue[{Sqrt[1+EulerPhi[n]],Sqrt[1+DivisorSigma[1,n]]},IntegerQ],1,0],{n,130}] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Dec 22 2018 *)

%o (Scheme) (define (A296213 n) (* (A010052 (+ 1 (A000010 n))) (A010052 (+ 1 (A000203 n)))))

%o (define (A296213 n) (if (zero? (A010052 (+ 1 (A000010 n)))) 0 (A010052 (+ 1 (A000203 n)))))

%K nonn

%O 1

%A _Antti Karttunen_, Dec 08 2017

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 October 13 20:38 EDT 2019. Contains 327981 sequences. (Running on oeis4.)