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A120450 Number of ways to express a prime p as 2*p1 + 3*p2, where p1, p2 are primes or 1. 1

%I

%S 0,0,1,1,1,2,2,2,2,2,2,3,3,4,3,3,3,5,4,4,4,4,4,4,6,3,5,4,4,4,6,5,5,5,

%T 5,7,5,6,6,6,6,7,5,6,7,6,7,9,8,8,6,7,7,8,7,9,6,10

%N Number of ways to express a prime p as 2*p1 + 3*p2, where p1, p2 are primes or 1.

%C It seems that every prime p > 3 can be expressed as 2*p1 + 3*p2, where p1, p2 are primes or 1. I have tested it for the first 1500 primes (up to 12553) and it is true.

%e a(11)=2 because we can write 31 (the 11th prime) as 2* 5 + 3* 7 OR 2* 11 + 3* 3

%e a(12)=3 because we can write 37 (the 12th prime) as 2* 2 + 3* 11 OR 2* 11 + 3* 5 OR 2* 17 + 3* 1

%K nonn

%O 1,6

%A _Vassilis Papadimitriou_, Jul 20 2006

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Last modified October 21 01:48 EDT 2021. Contains 348137 sequences. (Running on oeis4.)