%I #6 Jun 06 2021 09:03:36

%S 1,3,7,21,381,903,921,2667,5789,6447,17367,18543,73703,114681,116967,

%T 208443,221109,277221,746781,797349,818769,855141,871347,1459101,

%U 2205609,2354961,5090367,5331669,5692701,6099429,7611387,8710041

%N Numbers k such that k^3 divides 20^(k^2) + 1.

%Y Cf. A127263 (k^3 divides 2^(k^2) + 1).

%Y Cf. A128678, A128679, A128680, A128681, A128682, A128683, A128684, A128685.

%Y Cf. A177813, A177814, A177816, A177817, A177818, A177819, A177820.

%Y Cf. A128677 (least k > p such that (k*p)^3 divides (p-1)^(k*p)^2+1, where p = prime(n) > 2).

%K nonn

%O 1,2

%A _Alexander Adamchuk_, May 14 2010