A331373 Decimal expansion of Sum_{k>=2} 1/(k! - 1).

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

Offset: 1

Author

Amiram Eldar, May 03 2020

Keywords

• nonn
• cons

Comments

Erdős was interested in the question whether this constant is irrational.

Examples

			1.25349875569995347164336093790579894036923220833201...
		

References

• Paul Erdős, Some of my favourite unsolved problems, in A. Baker, B. Bollobás and A. Hajnal (eds.), A tribute to Paul Erdős, Cambridge University Press, 1990, p. 470.

Links

• Paul Erdős, On the irrationality of certain series: problems and results, in Alan Baker (ed.), New Advances in Transcendence Theory, Cambridge University Press, 1988, p. 102.
• Paul Erdős and Ronald L. Graham, Old and new problems and results in combinatorial number theory, L'enseignement Mathématique, Université de Genève, 1980, p. 62.

Crossrefs

Cf. A033312, A331372, A327826.

Programs

Mathematica

RealDigits[Sum[1/(k! - 1), {k, 2, 300}], 10, 100][[1]]

PARI

suminf(k=2, 1/(k!-1)) \\ Michel Marcus, May 03 2020