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.

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]

Links

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

Crossrefs

Cf. A075081, A062547, A111974, A005105

Sequence in context: A062090 A358975 A345898 * 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