# 9890881

$t_title is "9890881"

$t_subtitle is "(just those submitted by Yosei)"

$t_adjust_path is "/~caldwell/curios/"

$t_class is "composite"

$nunber_id is "19273"

$t_meta['description'] is "One of many pages of prime number
curiosities and trivia. This page discusses 9890881
Come explore a new prime today!"

Just showing those entries submitted by 'Yosei': (Click here to show all)

The smallest base-2 pseudoprime q such that 2q+1 is also a base-2 pseudoprime — a “Sophie Germain pseudoprime,” so to speak. Using Feitsma’s table, one can find two more such numbers < 2^64: 23456248059221 = R23 and 96076792050570581 = R29, where Rn = (4^n-1)/3 is a repunit in radix 4, which often yields a large Sophie Germain pseudoprime; 9890881 (a Carmichael number) is not of the same type. Can we find a “pseudo-Cunningham chain” of length 3? [Yosei]

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