A358361 Decimal expansion of the constant Sum_{j>=0} j!!/(2*j)!, where j!! indicates the double factorial of j.

1, 5, 8, 7, 7, 0, 2, 6, 4, 7, 7, 2, 7, 6, 6, 0, 5, 0, 7, 9, 7, 1, 8, 0, 1, 2, 6, 6, 2, 8, 5, 5, 5, 3, 7, 3, 2, 2, 3, 5, 4, 8, 6, 2, 3, 2, 4, 6, 7, 7, 2, 1, 2, 5, 2, 7, 5, 1, 6, 3, 2, 0, 4, 7, 3, 5, 6, 6, 5, 1, 0, 4, 0, 4, 6, 7, 1, 8, 6, 9, 5, 4, 9, 5, 5, 2, 2

Offset: 1

Author

Marco Ripà, Nov 12 2022

Keywords

• cons
• easy
• nonn

Comments

Sum_{j>=0} j!!/(2j)! converges since Sum_{j>=0} j!!/j! converges by A143280 (and it is trivial to note that (2*j)! >= j! for any positive integer j).

Examples

			1.587702647727...
		

Links

• Eric Weisstein's World of Mathematics, Double Factorial.

Crossrefs

Cf. A006882, A010050, A143280, A264152.

Programs

Mathematica

RealDigits[1 + Sum[(i)!!/(2i)!, {i,1,200}], 10, 105][[1]]

Formula

Equals Sum_{j>=0} A006882(j)/A010050(j).

Equals Sum_{j>=0} 1/(A264152(j)*j!).