A124276 - OEIS

A124276

Terms k of A068563 such that k/2 is not a term of A068563.

1, 6, 18, 20, 42, 54, 60, 100, 126, 136, 156, 162, 180, 220, 294, 300, 342, 378, 408, 420, 468, 486, 500, 540, 620, 660, 680, 780, 820, 882, 900, 1026, 1092, 1100, 1134, 1224, 1260, 1314, 1332, 1404, 1458, 1500, 1620, 1806, 1860, 1980, 2028, 2040, 2058, 2100

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OFFSET

1,2

COMMENTS

A068563 are the numbers n such that 2^n (mod n) = 4^n (mod n). If k is in the sequence A068563 then 2k is also in the sequence A068563, but if 2m is in the sequence A068563 m is not necessarily a term of the sequence A068563.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

EXAMPLE

A068563 begins 1, 2, 4, 6, 8, 12, 16, 18, 20, 24, 32, 36, 40, 42, ... .

Thus a(0) = 1, a(1) = 6, a(2) = 18, a(3) = 20, a(4) = 42 because 1/2, 3, 9, 10, 21 are not the terms of A068563.

MAPLE

a:= proc(n) option remember; local k;

for k from `if`(n=1, 1, a(n-1)+1)

while (2&^k mod k <> 4&^k mod k) or

(irem(k, 2, 'r')=0 and (2&^r mod r = 4&^r mod r))

do od; k

end: