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

1,1

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.

Links

Table of n, a(n) for n=1..52.

Prog

(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 */

Crossrefs

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

Sequence in context: A247439 A183635 A116223 * A235198 A235191 A076331

Adjacent sequences: A124238 A124239 A124240 * A124242 A124243 A124244

Keyword

nonn

Author

Alexander Adamchuk, Oct 22 2006, Oct 27 2006

Extensions

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

Status

approved