A124241 Terms of A068563 that are not terms of A124240.

136, 408, 620, 680, 820, 1224, 1240, 1314, 2040, 2312, 2460, 2480, 2628, 2856, 3100, 3400, 3672, 3924, 3942, 4100, 4112, 4656, 4960, 5304, 5334, 5784, 6120, 6200, 6820, 6936, 7380, 7480, 7848, 7884, 8224, 8568, 9020, 9060, 9198, 9492, 9920, 10200, 10668, 11016, 11560, 11568, 11826, 12300, 12336, 12400, 13140, 13640

Offset: 1

Author

Alexander Adamchuk, Oct 22 2006, Oct 27 2006

Keywords

• nonn

Comments

A068563 contains A124240 as a subsequence. This sequence gives their set difference.

Note that a(2) = 3*a(1) and a(4) = 5*a(1). a(6) = 1224 = 9*a(1), a(7) = 1240 = 2*a(3), a(8) = 1314, a(9) = 2040 = 15*a(1), a(10) = 2312 = 17*a(1), a(11) = 2460 = 3*a(5), a(12)= 2480 = 4*a(3), a(13) = 2856 = 21*a(1). Numbers k such that there exists a(n) = k*a(1) are k = {1, 3, 5, 9, 15, 17, 21, ...}.

Many but not all terms belong to A124276.

Crossrefs

Cf. A124240, A124239, A068563, A124276, A064896.

Programs

PARI

for(n=1,10^5, m=n\2^valuation(n,2); if( Mod(n,znorder(Mod(2,m))), next); p=factor(n)[,1]; g=1; for(i=1,#p, if( Mod(n,p[i]-1), g=0; break) ); if(g,next); print1(n,", ") ) /* Alekseyev */

Extensions

a(13) corrected and terms a(14) onward provided by Max Alekseyev, Aug 25 2013