This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A248861 #29 Jul 05 2024 02:02:43 %S A248861 1,2,8,36,128,225,289,578,900,2025,2601,3600,10404,32768,41616,45369, %T A248861 57600,242064,665856,725904,783225,1134225,1140624,1782225,1988100, %U A248861 2903616,3132900,4862025,6155361,6275025,7128900,7868025,8625969,10208025,13505625 %N A248861 Numbers k such that phi(k)^phi(k) == 1 (mod sigma(k)). %C A248861 2^m is a term of the sequence if and only if m=2^j-1 where j is a nonnegative integer. Hence the sequence is infinite. %C A248861 289 is a term of the sequence which is of the form p^2 where p is prime. What is the next such term? %C A248861 578 is a term of the sequence which is not of the form 2^m or m^2. What is the next such term? %C A248861 A248862 gives primes p such that 900*p^2 is a term of the sequence. %C A248861 Subsequence of A055008. - _Jason Yuen_, Jul 01 2024 %H A248861 Jason Yuen, <a href="/A248861/b248861.txt">Table of n, a(n) for n = 1..10000</a> %t A248861 Prepend[Select[Range[30000], Mod[EulerPhi[#]^EulerPhi[#], DivisorSigma[1, #]] == 1 &], 1] (* _Michael De Vlieger_, Dec 13 2014 *) %o A248861 (PARI) isok(n) = my(in = eulerphi(n)); lift(Mod(in, sigma(n))^in - 1) == 0; \\ _Michel Marcus_, Dec 13 2014 %Y A248861 Cf. A000010, A000203, A177006, A248862, A055008. %K A248861 nonn %O A248861 1,2 %A A248861 _Farideh Firoozbakht_, Dec 12 2014