A393802 - OEIS

A393802

Decimal expansion of 2 - 22/(5*sqrt(5)).

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

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OFFSET

0,2

COMMENTS

This constant gives the linear asymptotic coefficient of the variance of the number of hairpins in an RNA secondary structure on a number n of vertices tending to infinity (see Theorem 3 in Bu, Kauers, and Zeilberger).

LINKS

Table of n, a(n) for n=0..100.

AJ Bu, Manuel Kauers, and Doron Zeilberger, Statistical Analysis of Hairpins and BasePairs in RNA Secondary Structures, arXiv:2602.19255 [math.CO], 2026.

FORMULA

Minimal polynomial: 125*x^2 - 500*x + 16.

EXAMPLE

0.032260179800185067159927171516476912812255843541...

MATHEMATICA

Join[{0}, RealDigits[2-22/(5Sqrt[5]), 10, 100][[1]]]

CROSSREFS

Cf. A002163, A020837, A393800, A393801.

Sequence in context: A371942 A259967 A007567 * A093055 A285733 A106335

Adjacent sequences: A393799 A393800 A393801 * A393804 A393805 A393806

KEYWORD

nonn,cons,easy

AUTHOR

Stefano Spezia, Feb 27 2026

STATUS

approved