Just entered 151026*5^110-1 into msieve:
prp41 factor: 19094485960440215874363137033854288407797
prp42 factor: 609318305575000443064617648157915891177117
So a relatively hard composite for ECM.
Lars:
If you want, you can provide a list of the smallest composites without factors (maybe up to 100 digits).
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