Phi21(2^21^m)
Phi21(x) = x12-x11+x9-x8+x6-x4+x3-x+1
          
Phi21(2^21^m) = 4096^21^m-2048^21^m+512^21^m-256^21^m+64^21^m-16^21^m+8^21^m-2^21^m+1
Shanks(21)


0 7 * 337
1 126127 * 309583 * 5828257 * 4487533753346305838985313 * 7086423574853972147970086088434689
2 C(1594)
3 2793967688877020839 * C(33436)



(0) 2*21^1
7 exception
337-1 = 2^4 * 3 * 7

(1) 2*21^2
126127-1 = 2 * 3^2 * 7^2 * 11 * 13
309583-1 = 2 * 3^5 * 7^2 * 13
5828257-1 = 2^5 * 3^2 * 7^3 * 59
4487533753346305838985313-1 = 2^5 * 3^3 * 7^2 * 3049 * 80239 * 433266363247
7086423574853972147970086088434689-1 = 2^10 * 3^2 * 7^2 * 37 * 424118129700210343552861261

(3) 2*21^4
2793967688877020839-1 = 2 * 3^4 * 7^4 * 13 * 170633 * 3238231