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Number of ways to express n as p+2a^2; p = 1 or prime, a >= 0.
6

%I #17 Jul 22 2021 09:17:02

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

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

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

%N Number of ways to express n as p+2a^2; p = 1 or prime, a >= 0.

%H T. D. Noe, <a href="/A046920/b046920.txt">Table of n, a(n) for n=1..10000</a>

%H L. Hodges, <a href="https://www.jstor.org/stable/2690477">A lesser-known Goldbach conjecture</a>, Math. Mag., 66 (1993), 45-47.

%H <a href="/index/Go#Goldbach">Index entries for sequences related to Goldbach conjecture</a>

%o (Haskell)

%o a046920 n = length $ filter ((\x -> x == 1 || a010051 x == 1) . (n -)) $

%o takeWhile (< n) a001105_list

%o -- _Reinhard Zumkeller_, Apr 03 2013

%Y Cf. A042978, A046921, A046922, A046923, A060003, A143539.

%Y Cf. A016067, A008578, A010051, A001105.

%K nonn

%O 1,3

%A _David W. Wilson_