Somer pseudoprime
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A Somer pseudoprime is an odd composite number based on another number. They can be obtained by this process from a number D:
- (D2) − (2D − 1) + 1 if D is odd
The first nine Somer pseudoprimes thus are
These numbers are always odd, and one notices the digit pattern 1-3-9-5-5-5-9-3-1. This type of pseudoprime is often confused with Somer-Lucas pseudoprimes, which also have a number P and are formed by a Lucas sequence. The symbol for a Somer number is SQ.
This is sequence A085046 of the On-Line Encyclopedia of Integer Sequences.
