OFFSET
1,1
COMMENTS
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.
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
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