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A172095
Integers n such that n-1,n,n+1 have few distinct primes: n=p^r, p odd prime, and (n^2-1)/8 divisible by at most two distinct prime factors.
0
3, 5, 7, 9, 11, 13, 17, 19, 27, 37, 53, 107, 163, 243, 2187, 2917, 4373, 8747, 1594323, 86093443
OFFSET
1,1
COMMENTS
Note the terms 3^1=3, 3^2=9, 3^3=27, 3^5=243, 3^7=2187, and 3^13=1594323. The other listed terms are prime.
Next term > 2^2000. [From Max Alekseyev]
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Dino Lorenzini (lorenzin(AT)uga.edu), Jan 25 2010
EXTENSIONS
Edited and missing terms 3, 5, 9, 17 added by Max Alekseyev, Feb 16 2011
STATUS
approved