A167506 - OEIS

%I #7 Nov 11 2019 09:25:08

%S 2,2,3,4,5,2,6,7,6,3,5,1,10,1,3,8,10,2,7,4,3,2,9,1,5,1,5,5,6,2,13,6,3,

%T 1,9,5,10,2,5,7,13,1,11,6,4,0,12,1,8,3,7,9,11,1,7,7,4,2,11,1,11,2,9,6,

%U 6,1,13,8,8,1,9,2,13,0,5,4,12,1,11,2,10,3,13,2,8,2,4,6,9,1,6,7,4,1,8,1,9,1

%N Number of m >= 0, m <=n such that 2^(n-m) 3^m + 1 or 2^(n-m) 3^m - 1 is prime.

%C M. Underwood observed that for all primes p < 3187 we have a(p) > 1, and asks whether there is a prime such that a(p) = 0. (This is equivalent to A167504(p) = A167505(p) = 0.)

%H M. Underwood, <a href="http://groups.yahoo.com/group/primenumbers/message/21119">2^a*3^b one away from a prime</a>. Post to primenumbers group, Nov. 19, 2009.

%H Mark Underwood, Jens Kruse Andersen, <a href="/A167504/a167504.txt">2^a*3^b one away from a prime</a>, digest of 3 messages in primenumbers Yahoo group, Nov 19, 2009.

%F max { A167504(n), A167505(n) } <= A167506(n) <= A167504(n)+A167505(n)

%o (PARI) A167505(n)=sum( b=0,n, ispseudoprime(3^b<<(n-b)-1) || ispseudoprime(3^b<<(n-b)+1))

%Y Cf. A167504, A167505.

%K nonn

%O 1,1

%A _M. F. Hasler_, Nov 19 2009