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A179282 Numbers n such that 2^n-2 and 2^n+2 are not squarefree. 0
1, 22, 31, 64, 79, 91, 106, 111, 148, 151, 190, 205, 211, 232, 235, 271, 274, 311, 316, 331, 341, 358, 391, 400, 442, 451, 466, 484, 511, 526 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Most (not all) of the terms are of the form:

x^2-y^2, for x>y>0.

31=16^2-15^2,

64=10^2-6^2=17^2-15^2,

79=40^2-39^2,

91=10^2-3^2=46^2-45^2,

111=20^2-17^2=56^2-55^2,

148=11^2-3^3=38^2-36^2,

151=76^2-75^2,

205=23^2-18^2=103^2-102^2,

211=106^2-105^2.

LINKS

Table of n, a(n) for n=1..30.

EXAMPLE

2^22-2=2*7^2*127*337, 2^22+2=2*3^2*43*5419.

MATHEMATICA

Select[Range@211, !(SquareFreeQ[2^#-2]||SquareFreeQ[2^#+2])&]

CROSSREFS

Cf. A005117.

Sequence in context: A129073 A092215 A239431 * A106555 A106557 A142347

Adjacent sequences:  A179279 A179280 A179281 * A179283 A179284 A179285

KEYWORD

nonn,hard,more

AUTHOR

Vladimir Joseph Stephan Orlovsky, Mar 22 2011

EXTENSIONS

a(14)-a(30) from D. S. McNeil, Mar 23 2011

STATUS

approved

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Last modified November 15 11:35 EST 2018. Contains 317238 sequences. (Running on oeis4.)