A049006 -id:A049006 - cp's OEIS frontend

A073226 Decimal expansion of e^e.

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

Offset: 2

Rick L. Shepherd, Jul 21 2002

Given z > 0, there exist positive real numbers x < y, with x^y = y^x = z, if and only if z > e^e. In that case, 1 < x < e < y and (x, y) = ((1 + 1/t)^t, (1 + 1/t)^(t+1)) for some t > 0. (For example, t = 1 gives 2^4 = 4^2 = 16 > e^e.) Proofs of these classical results and applications of them are in Marques and Sondow (2010).
e^e = lim_{n->infinity} ((n+1)/n)^((n+1)^(n+1)/n^n), n > 0 an integer; cf. [Vernescu] wherein it is also stated that the assertions of the previous comment above were proved by Alexandru Lupas in 2006. - L. Edson Jeffery, Sep 18 2012
A weak form of Schanuel's Conjecture implies that e^e is transcendental--see Marques and Sondow (2012).

			15.15426224147926418976043027262991190552854853685613976914...

Harry J. Smith, Table of n, a(n) for n = 2..20000
D. Marques and J. Sondow, The Schanuel Subset Conjecture implies Gelfond's Power Tower Conjecture, arXiv:1212.6931 [math.NT], 2012-2013.
Simon Plouffe, exp(E) to 2000 places
J. Sondow and D. Marques, Algebraic and transcendental solutions of some exponential equations, Annales Mathematicae et Informaticae 37 (2010) 151-164.
A. Vernescu, About the use of a result of Professor Alexandru Lupas to obtain some properties in the theory of the number e, Gen. Math., Vol. 15, No. 1 (2007), 75-80.

Cf. A073233 (Pi^Pi), A049006 (i^i), A001113 (e), A073227 (e^e^e), A004002 (Benford numbers), A056072 (floor(e^e^...^e), n e's), A072364 ((1/e)^(1/e)), A030178 (limit of (1/e)^(1/e)^...^(1/e)), A073229 (e^(1/e)), A073230 ((1/e)^e).

Exp(Exp(1)); // G. C. Greubel, May 29 2018

Mathematica
```
RealDigits[ E^E, 10, 110] [[1]]
```
PARI
```
exp(exp(1))
```

{ default(realprecision, 20080); x=exp(1)^exp(1)/10; for (n=2, 20000, d=floor(x); x=(x-d)*10; write("b073226.txt", n, " ", d)); } \\ Harry J. Smith, Apr 30 2009

Equals Sum_{n>=0} e^n/n!. - Richard R. Forberg, Dec 29 2013

Equals Product_{n>=0} e^(1/n!). - Amiram Eldar, Jun 29 2020

A073233 Decimal expansion of Pi^Pi.

Original entry on oeis.org

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

Offset: 2

Rick L. Shepherd, Jul 21 2002

A weak form of Schanuel's Conjecture implies that Pi^Pi is transcendental--see Marques and Sondow (2012).

			36.4621596072079117709908260226...

Harry J. Smith, Table of n, a(n) for n = 2..20000
D. Marques and J. Sondow, The Schanuel Subset Conjecture implies Gelfond's Power Tower Conjecture, arXiv:1212.6931 [math.NT], 2012-2013.

Cf. A000796 (Pi), A073234 (Pi^Pi^Pi), A073237 (ceil(Pi^Pi^...^Pi), n Pi's), A073238 (Pi^(1/Pi)), A073239 ((1/Pi)^Pi), A073240 ((1/Pi)^(1/Pi)), A073243 (limit of (1/Pi)^(1/Pi)^...^(1/Pi)), A073236 (Pi analog of A004002).
Cf. A073226 (e^e).
Cf. A049006 (i^i), A116186 (real part of i^i^i).
Cf. A194555 (real part of i^e^Pi).

RealDigits[N[Pi^Pi,200]] (* Vladimir Joseph Stephan Orlovsky, May 27 2010 *)

PARI
```
Pi^Pi
```

{ default(realprecision, 20080); x=Pi^Pi/10; for (n=2, 20000, d=floor(x); x=(x-d)*10; write("b073233.txt", n, " ", d)); } \\ Harry J. Smith, Apr 30 2009

A042972 Decimal expansion of i^(-i), where i = sqrt(-1).

Original entry on oeis.org

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

Offset: 1

Marvin Ray Burns

Square root of Gelfond's constant (A039661). Since Gelfond's constant e^Pi is transcendental, e^(Pi/2) is transcendental. - Daniel Forgues, Apr 15 2011
The complex sequence (...((((i)^i)^i)^i)^...) (n pairs of brackets) is periodic with period 4 and the first four entries are i, e^(-Pi/2), -i, e^(+Pi/2). See A049006 for e^(-Pi/2). - Wolfdieter Lang, Apr 27 2013
A solution of x^i + x^(-i) = 0. In fact, x = Exp(Pi/2 + k*Pi), where k is any integer. - Robert G. Wilson v, Feb 04 2014

			4.81047738096535165547303566670383312639017087466453494002...

Nathaniel Johnston, Table of n, a(n) for n = 1..10000
H. S. Uhler, On the numerical value of i^i, Amer. Math. Monthly, 28 (1921), 114-116.
Index entries for transcendental numbers

Cf. A049006.

SetDefaultRealField(RealField(110)); R:= RealField(); Exp(Pi(R)/2); // G. C. Greubel, Feb 17 2019

evalf[110](I^(-I)); # Muniru A Asiru, Feb 17 2019

RealDigits[Re[I^(1/I)], 10, 100][[1]] (* Alonso del Arte, Oct 31 2011 *)
RealDigits[ Exp[Pi/2], 10, 111][[1]] (* Robert G. Wilson v, Apr 08 2014 *)

default(realprecision, 110); exp(Pi/2) \\ Nathaniel Johnston, Apr 15 2011 (modified by G. C. Greubel, Feb 17 2019)

numerical_approx(exp(pi/2), digits=110) # G. C. Greubel, Feb 17 2019

Equals i^(-i) = i^(1/i) = e^(Pi/2).

Also (((i)^i)^i)^i. See a comment above on such powers. - Wolfdieter Lang, Apr 27 2013

a(100) corrected by Nathaniel Johnston, Apr 15 2011

A198683 Number of distinct values taken by i^i^...^i (with n i's and parentheses inserted in all possible ways) where i = sqrt(-1) and ^ denotes the principal value of the exponential function.

Original entry on oeis.org

1, 1, 2, 3, 7, 15, 34, 77, 187, 462, 1152

Offset: 1

Vladimir Reshetnikov, Oct 28 2011

There are C(n-1) ways of inserting the parentheses (where C is a Catalan number, A000108), but not all arrangements produce different values.
At n=10, the expression i^(i^(((i^i)^i)^(i^((i^i)^(i^i))))) evaluates to a large complex number, C = -6.795047376...*10^34 - i*6.044219499...*10^34; as a result, i^C, which arises at n=11, is very large, having a magnitude of e^((-Pi/2)*(-6.044219499...*10^34)) = 4.1007...*10^41232950809707420597749203381002924. - Jon E. Schoenfield, Nov 21 2015
Note that if a is a REAL positive number, the number of different values of a^a^...^a with n a's is at most A000081(n). But this relies on the identity (x^y)^z = (x^z)^y = x^(yz), which is not always true for complex numbers with the principal value of the power function. Thus if Y = ((i^i)^i)^i, we have (i^i)^Y / (i^Y)^i = exp(-2 Pi). - Robert Israel, Nov 27 2015 [So for the present sequence, we know a(n) <= A000108(n-1), but we do not know that a(n) <= A000081(n). - N. J. A. Sloane, Nov 28 2015]

			a(1) = 1: there is one value, i.
a(2) = 1: there is one value, i^i = exp(i Pi / 2)^i = exp(-Pi/2) = 0.2079...
a(3) = 2: there are two values: (i^i)^i = i^(-1) = 1/i = -i and i^(i^i) = i^0.2079... = exp(0.2079... i Pi / 2) = 0.9472... + 0.3208... i.
a(4) = 3: there are 5 possible parenthesizations but they give only 3 distinct values: i^(i^(i^i)), i^((i^i)^i) = ((i^i)^i)^i, (i^i)^(i^i) = (i^(i^i))^i.

R. K. Guy and J. L. Selfridge, The nesting and roosting habits of the laddered parenthesis, Amer. Math. Monthly 80 (8) (1973), 868-876.
R. K. Guy and J. L. Selfridge, The nesting and roosting habits of the laddered parenthesis (annotated cached copy)
MathOverflow, Discussion of related questions
Jon E. Schoenfield, Tables for n = 1..11 listing all A000108(n-1) ways of inserting the parentheses and identifying the ways that do not yield duplicated values

Cf. A000081, A000108, A002845, A049006, A077589, A077590.

iParens[1] = {I}; iParens[n_] := iParens[n] = Union[Flatten[Table[Outer[Power, iParens[k], iParens[n - k]], {k, n - 1}]], SameTest -> Equal]; Table[Length[iParens[n]], {n, 10}]

a(11) and a(12) (unconfirmed) from Alonso del Arte, Nov 17 2011

a(12) is said to be either 2919 or 2926. The value will not be included in the data section until it has been confirmed. - N. J. A. Sloane, Nov 26 2015

A073244 Decimal expansion of Pi - e.

Original entry on oeis.org

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

Offset: 0

Rick L. Shepherd, Jul 21 2002

			0.42331082513074800310235591192...

Cf. A059742 (Pi+e), A000796 (Pi), A001113 (e), A019609 (Pi*e), A061382 (Pi/e), A061360 (e/Pi), A039661 (e^Pi), A059850 (Pi^e), A073233 (Pi^Pi), A073226 (e^e), A049006 (i^i = e^(-Pi/2)).

Cf. A110564 for continued fraction for Pi - e.

RealDigits[N[Pi-E,6! ]][[1]] (* Vladimir Joseph Stephan Orlovsky, Jun 18 2009 *)

PARI
```
Pi-exp(1)
```

A077589 Decimal expansion of real part of the infinite power tower of i.

Original entry on oeis.org

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

Offset: 0

Eric W. Weisstein, Nov 07 2002

This is the real part of i^i^i^i^i^i...

			0.43828293672703211162697516355126482426789735164639460360922124049579153222269568...

Steven R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, Section 6.11, p. 449.

Eric Weisstein's World of Mathematics, i.
Eric Weisstein's World of Mathematics, Power Tower.

Cf. A049006, A077590 (imaginary part).

evalf(Re(2*I*LambertW(-I*Pi/2)/Pi), 137);  # Alois P. Heinz, Dec 12 2023

Prepend@@RealDigits[Re[ -ProductLog[ -Log[I]]/Log[I]], 10, 150]

z=(1+I)/2;e=.1^default(realprecision);until(e>abs(z-z-=(z-I^z)/(1-I^(z+1)*Pi/2)),);digits(real(z)\e) \\ M. F. Hasler, May 17 2018

The value is 2 (i/Pi) W(-i Pi/2) = 0.4382829... + i 0.360592..., where W denotes the principal branch of the Lambert W function. - David W. Cantrell, Nov 23 2007

A077590 Decimal expansion of imaginary part of the infinite power tower of i.

Original entry on oeis.org

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

Offset: 0

Eric W. Weisstein, Nov 07 2002

			0.36059247187138548595294052690600065382657703078602700474145129838046019521150773...

Steven R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, Section 6.11, p. 449.

Eric Weisstein's World of Mathematics, i.
Eric Weisstein's World of Mathematics, Power Tower.

Cf. A049006, A077589 (real part).

evalf(Im(2*I*LambertW(-I*Pi/2)/Pi), 139);  # Alois P. Heinz, Dec 12 2023

Prepend@@RealDigits[Im[ -ProductLog[ -Log[I]]/Log[I]], 10, 150]

z=(1+I)/2;e=.1^default(realprecision);until(e>abs(z-z-=(z-I^z)/(1-I^(z+1)*Pi/2)),);digits(imag(z)\e) \\ M. F. Hasler, May 17 2018

A093580 Decimal expansion of e^(-Pi).

Original entry on oeis.org

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

Offset: 0

Mohammad K. Azarian, May 14 2004

Also, decimal expansion of (-1)^i. - Rick L. Shepherd, Jul 09 2013

Also, the greatest real value of z that minimizes z^i + z^(-i). - Colin Linzer, Nov 21 2024

			0.04321391826377224977441773717172801127572810981...

Harry J. Smith, Table of n, a(n) for n = 0..20000
H. S. Uhler, On the numerical value of i^i, Amer. Math. Monthly, 28 (1921), 114-116.
Index entries for transcendental numbers.

Cf. A039661, A001113, A000796, A049006.

Join[{0}, RealDigits[E^-Pi, 10, 105][[1]]] (* Harvey P. Dale, Apr 25 2012 *)

{ default(realprecision, 20080); x=10*exp(-Pi); for (n=0, 20000, d=floor(x); x=(x-d)*10; write("b093580.txt", n, " ", d)); } \\ Harry J. Smith, Jun 19 2009

Equals 1/A039661 = A049006^2. - Hugo Pfoertner, Nov 22 2024

A202501 Decimal expansion of x satisfying x=e^(-Pi*x/2).

Original entry on oeis.org

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

Offset: 0

Clark Kimberling, Dec 20 2011

See A202348 for a guide to related sequences. The Mathematica program includes a graph.

Also the only solution of x=I^(x*I), since I^I = exp(-Pi/2). Also the infinite power tower (tetration) of I^I, i.e., the convergent sequence I^(I*I^(I*I^(...(I*I^I)...))). Also LambertW(Pi/2)/(Pi/2). - Stanislav Sykora, Nov 06 2013

			x=0.474540999512651123017467944048212451149107680...

Stanislav Sykora, Table of n, a(n) for n = 0..2000
Steven R. Finch, Tauberian Constants, August 30, 2004 [Cached copy, with permission of the author]

Cf. A202348, A049006, A231095 (comment).

u = -Pi/2; v = 0;
f[x_] := x; g[x_] := E^(u*x + v)
Plot[{f[x], g[x]}, {x, -1, 1}, {AxesOrigin -> {0, 0}}]
r = x /. FindRoot[f[x] == g[x], {x, .4, .5}, WorkingPrecision -> 110]
RealDigits[r]    (* A202501 *)
RealDigits[ 2*ProductLog[Pi/2]/Pi, 10, 99] // First (* Jean-François Alcover, Feb 27 2013 *)

lambertw(Pi/2)/(Pi/2) \\ Stanislav Sykora, Nov 06 2013

A305200 Decimal expansion of the real part of continued exponential of i.

Original entry on oeis.org

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

Offset: 0

Keerthi Vasan Gopala, May 27 2018

			0.576412723031435283148289239887068476278...

This is the real part of e^(i*e^(i*e^(i...))).

Eric Weisstein's World of Mathematics, Lambert W-Function
Wikipedia, Lambert W function

Cf. A049006, A077589, A077590, A191719, A305202.

RealDigits[Re[I*LambertW[-I]],10,120][[1]] (* Harvey P. Dale, Dec 01 2018 *)
RealDigits[x /. FindRoot[E^(x*Tan[x]) == Cos[x]/x, {x, 1/2}, WorkingPrecision -> 120]][[1]] (* Vaclav Kotesovec, Oct 02 2021 *)

Equals Re(i*LambertW(-i)). - Alois P. Heinz, May 27 2018
From Vaclav Kotesovec, Oct 02 2021: (Start)
Root of the equation exp(x*tan(x)) = cos(x)/x.
Equals Im(LambertW(i)). (End)

More digits from Alois P. Heinz, May 27 2018

cp's OEIS Frontend

A073226 Decimal expansion of e^e.

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A073233 Decimal expansion of Pi^Pi.

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A042972 Decimal expansion of i^(-i), where i = sqrt(-1).

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A198683 Number of distinct values taken by i^i^...^i (with n i's and parentheses inserted in all possible ways) where i = sqrt(-1) and ^ denotes the principal value of the exponential function.

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A073244 Decimal expansion of Pi - e.

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A077589 Decimal expansion of real part of the infinite power tower of i.

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A077590 Decimal expansion of imaginary part of the infinite power tower of i.

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