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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 (list; graph; refs; listen; history; text; internal format)
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]

LINKS

Table of n, a(n) for n=1..20.

CROSSREFS

Cf. A075081, A062547, A111974, A005105

Sequence in context: A326581 A050150 A062090 * A309361 A133854 A239008

Adjacent sequences:  A172092 A172093 A172094 * A172096 A172097 A172098

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

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Last modified November 12 19:33 EST 2019. Contains 329078 sequences. (Running on oeis4.)