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 A212844 #45 May 20 2021 10:55:31 %S A212844 0,0,2,0,3,4,1,0,5,6,8,4,8,2,2,0,8,4,8,4,11,16,8,16,3,16,23,8,8,16,8, %T A212844 0,32,16,2,4,8,16,32,24,8,4,8,20,23,16,8,16,22,46,32,12,8,4,7,16,32, %U A212844 16,8,4,8,16,32,0,63,58,8,64,32,36,8,40,8,16,47 %N A212844 a(n) = 2^(n+2) mod n. %C A212844 Also a(n) = x^x mod (x-2), where x = n+2. %C A212844 Indices of 0's: 2^k, k>=0. %C A212844 Indices of 1's: 7, 511, 713, 11023, 15553, 43873, 81079, 95263, 323593, 628153, 2275183, 6520633, 6955513, 7947583, 10817233, 12627943, 14223823, 15346303, 19852423, 27923663, 28529473, ... %C A212844 Conjecture: every integer k >= 0 appears in a(n) at least once. %C A212844 Each number below 69 appears at least once. Some large first occurrences: a(39806401) = 25, a(259274569) = 33, a(10571927) = 55, a(18039353) = 81. - _Charles R Greathouse IV_, Jul 21 2015 %H A212844 Harvey P. Dale, <a href="/A212844/b212844.txt">Table of n, a(n) for n = 1..1000</a> %F A212844 a(n) = 2^(n+2) mod n. %e A212844 a(3) = 2^5 mod 3 = 32 mod 3 = 2. %p A212844 A212844 := proc(n) %p A212844 modp( 2&^ (n+2),n) ; %p A212844 end proc: # _R. J. Mathar_, Jul 24 2012 %t A212844 Table[PowerMod[2, n+2, n], {n, 79}] (* _Alonso del Arte_, Jul 22 2012 *) %o A212844 (Python) %o A212844 for n in range(1,99): %o A212844 print(2**(n+2) % n, end=',') %o A212844 (PARI) A212844(n)=lift(Mod(2,n)^(n+2)) \\ _M. F. Hasler_, Jul 23 2012 %Y A212844 Cf. A000312, A015910, A062173, A112983, A213381, A213859. %K A212844 nonn %O A212844 1,3 %A A212844 _Alex Ratushnyak_, Jul 22 2012