A261963 Smallest number that can be written as the sum of a Sophie Germain prime (A005384) and a practical number (A005153) in exactly n ways.

2, 3, 6, 23, 31, 35, 65, 59, 95, 131, 173, 233, 203, 239, 257, 299, 317, 323, 473, 443, 635, 563, 671, 719, 809, 701, 779, 839, 803, 1109, 971, 1049, 1139, 1343, 1103, 1409, 1433, 1607, 1481, 1499, 1559, 1523, 1769, 1679, 1643, 2069, 2063, 2309, 2111, 2141

Offset: 0

Author

Felix Fröhlich, Sep 06 2015

Keywords

• nonn

Examples

			23 can be written as the sum of a Sophie Germain prime and a practical number in the following three ways: 3 + 20, 5 + 18, 11 + 12.
Since 23 is the smallest number that can be expressed like that in exactly three ways, a(3) = 23.
		

Crossrefs

Cf. A005153, A005384, A209253.

Programs

PARI

\\ First define the function is_a005153(n) as in A005153
is_a005384(n) = ispseudoprime(n) && ispseudoprime(2*n+1)
count(n) = x=1; y=n-1; i=0; while(y > n/2, if((is_a005153(x) && is_a005384(y)) || (is_a005153(y) && is_a005384(x)), i++); x++; y--); i
a(n) = k=2; while(count(k)!=n, k++); k