A064915 - OEIS

A064915

Positive integers n that are not of the form p + q * a^2, where p and q are primes and a is the smallest prime not dividing n.

%I #6 Jun 24 2014 01:08:18

%S 1,2,3,4,5,6,7,8,9,10,12,14,16,18,22,24,26,28,30,36,42,48,54,60,66,72,

%T 77,84,90,96,102,108,114,120,126,174,180,210,240,270,300,330,420,630,

%U 840,1050,1260

%N Positive integers n that are not of the form p + q * a^2, where p and q are primes and a is the smallest prime not dividing n.

%C There are no other terms up to 10^7. Conjecture: There are no more terms in the sequence.

%t rep[ n_ ] := Module[ {a, q}, For[ a=2, GCD[ n, a ]!=1, a++, Null ]; For[ q=2, q a^2<n, q++, If[ PrimeQ[ q ]&&PrimeQ[ n-q a^2 ], Return[ True ] ] ]; False ]; Select[ Range[ 1, 10000 ], !rep[ # ]& ]

%Y Cf. A064653.

%K nonn

%O 1,2

%A _Dean Hickerson_, Oct 13 2001