A391855 - OEIS

%I #7 Dec 21 2025 20:01:57

%S 1,3,5,7,31,33,63,65,119,127,129,133,161,195,255,257,261,321,387,455,

%T 511,513,517,641,645,771,1023,1025,1029,1057,1281,1285,1539,1799,1823,

%U 1911,1991,2047,2049,2053,2081,2113,2561,2565,3075,3591,3647,4039,4095,4097,4101,4129,4161,4225,4229,4257,5121,5125,5153

%N Odd numbers k such that 19*k = A048720(m, k) for some m, where A048720 is carryless base-2 multiplication.

%H Antti Karttunen, <a href="/A391855/b391855.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Con#CongruCrossDomain">Index entries for sequences defined by congruent products between domains N and GF(2)[X]</a>.

%H <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>.

%H <a href="/index/Ca#CARRYLESS">Index entries for sequences related to carryless arithmetic</a>.

%F {Odd k such that A280500(19*k, k) = m for some m > 0}.

%o (PARI) is_A391855(k) = ((k%2) && (0==lift(Pol(binary(19*k)*Mod(1, 2)) % Pol(binary(k))*Mod(1, 2))));

%Y Row 19 of A391725. Odd terms of A391854.

%Y Cf. A048720, A280500.

%K nonn,base

%O 1,2

%A _Antti Karttunen_, Dec 21 2025