Deceptive Numbers

It's not surprising that I've not come across deceptive numbers before as they are quite light on the ground so to speak. Today, 27613 is the number associated with my diurnal age and it is a deceptive number but the previous such number was 24661 and the next will be 29431. So what constitutes a deceptive number? Here what Numbers Aplenty has to say:

Let us denote with \(R_k\) the repunit \(111\dots 1\) made of \(k\) ones.

It is known that every odd prime \(p\) divides the repunit \(R_{p-1}\).

R. Francis & T. Ray call a composite number \(n\) deceptive if it has the same property, i.e., if it divides the repunit \(R_{n-1}\).

For example, \(91=7 \times 13\) is deceptive because it divides \(R_{90}\).

Francis & Ray have proved that there are infinite deceptive numbers since, if \(n\)  is deceptive, then \(R_n\) is deceptive as well.

Every number greater than 2980 can be written as the sum of deceptive numbers.

Here are the deceptive numbers up to 100,001: 

91, 259, 451, 481, 703, 1729, 2821, 2981, 3367, 4141, 4187, 5461, 6533, 6541, 6601, 7471, 7777, 8149, 8401, 8911, 10001, 11111, 12403, 13981, 14701, 14911, 15211, 15841, 19201, 21931, 22321, 24013, 24661, 27613, 29341, 34133, 34441, 35113, 38503, 41041, 45527, 46657, 48433, 50851, 50881, 52633, 54913, 57181, 63139, 63973, 65311, 66991, 67861, 68101, 75361, 79003, 82513, 83119, 94139, 95161, 97273, 97681, 100001, ...

These numbers comprise OEIS A000864:

 A000864: deceptive nonprimes: composite numbers \(k\) that divide the repunit \(R_{k-1}\).