2,1

a(n) >= 3, = 3 if A002110(n) == 6 or 10 mod 16.

Whenever A000040(n) is in A003629, at least one of a(n) and a(n+1) is 3.

Robert Israel, Table of n, a(n) for n = 2..10000

MathOverflow question On quantities with no very small odd prime factors; a response to Wlodzimierz Holsztynski

A002110(2) = 2*3 = 6 and (6/2)^2-1 = 8 = 2^3 so a(2) = 3.

N:= 1000; # to get a(2) to a(N)

P:= 1:

for n from 2 to N do

P:= P * ithprime(n);

A[n]:= padic[ordp](P^2-1, 2);

od:

seq(A[n], n=2..N); # Robert Israel, Jun 02 2014

Cf. A002110.

Sequence in context: A075077 A196771 A266121 * A081361 A195132 A086181

Adjacent sequences: A243293 A243294 A243295 * A243297 A243298 A243299

nonn

Robert Israel, Jun 02 2014

approved