

A001146


a(n) = 2^(2^n).
(Formerly M1297 N0497)


42



2, 4, 16, 256, 65536, 4294967296, 18446744073709551616, 340282366920938463463374607431768211456, 115792089237316195423570985008687907853269984665640564039457584007913129639936
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OFFSET

0,1


COMMENTS

Or, write previous term in base 2, read in base 4.
a(1) = 2, a(n) = smallest power of 2 which does not divide the product of all previous terms.
Number of truth tables generated by boolean expressions of n variables.  C. Bradford Barber (bradb(AT)shore.net), Dec 27 2005
From Ross Drewe, Feb 13 2008: (Start)
Or, number of distinct nary operators in a binary logic. The total number of nary operators in a kvalued logic is T = k^(k^n), i.e., if S is a set of k elements, there are T ways of mapping an ordered subset of n elements from S to an element of S. Some operators are "degenerate": the operator has arity p, if only p of the n input values influence the output. Therefore the set of operators can be partitioned into n+1 disjoint subsets representing arities from 0 to n.
For n = 2, k = 2 gives the familiar Boolean operators or functions, C = F(A,B). There are 2^2^2 = 16 operators, composed of: arity 0: 2 operators (C = 0 or 1), arity 1: 4 operators (C = A, B, not(A), not(B)), arity 2: 10 operators (including wellknown pairs AND/NAND, OR/NOR, XOR/EQ). (End)
From José María Grau Ribas, Jan 19 2012: (Start)
Or, numbers that can be formed using the number 2, the power operator (^), and parenthesis. (End) [The paper by Guy and Selfridge (see also A003018) shows that this is the same as the current sequence.  N. J. A. Sloane, Jan 21 2012]
a(n) is the highest value k such that A173419(k) = n+1.  Charles R Greathouse IV, Oct 03 2012
Let b(0) = 8 and b(n+1) = the smallest number not in the sequence such that b(n+1)  Product_{i=0..n} b(i) divides b(n+1)*Product_{i=0..n} b(i). Then b(n) = a(n) for n > 0.  Derek Orr, Jan 15 2015


REFERENCES

D. E. Knuth, The Art of Computer Programming, Vol. 4A, Section 7.1.1, p. 79.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..12
A. V. Aho and N. J. A. Sloane, Some doubly exponential sequences, Fib. Quart., 11 (1973), 429437.
J. H. Conway, Sphere packings, lattices, codes and greed, pp. 4555 of Proc. Intern. Congr. Math., Vol. 2, 1994.
Jose María Grau and A. M. OllerMarcen On the last digit and the last nonzero digit of n^n in base b.
R. K. Guy and J. L. Selfridge, The nesting and roosting habits of the laddered parenthesis, Amer. Math. Monthly 80 (8) (1973), 868876.
R. Ondrejka, Exact values of 2^n, n=1(1)4000, Math. Comp., 23 (1969), 456.
Eric Weisstein's World of Mathematics, Irrationality Sequence, Quadratic Recurrence Equation, Coin Tossing.
Index entries for sequences of form a(n+1)=a(n)^2 + ...


FORMULA

a(n+1) = (a(n))^2.
1 = sum_{n>=0} a(n)/A051179(n+1) = 2/3 + 4/15 + 16/255 + 256/65535, ...; with partial sums: 2/3, 14/15, 254/255, 65534/65535, ...  Gary W. Adamson, Jun 15 2003
a(n) = A000079(A000079(n)).  Robert Israel, Jan 15 2015


MAPLE

A001146:=n>2^(2^n): seq(A001146(n), n=0..9); # Wesley Ivan Hurt, Sep 19 2014


MATHEMATICA

2^2^Range[0, 10] (* Harvey P. Dale, Jul 20 2011 *)


PROG

(MAGMA) [2^(2^n): n in [0..8]]; // Vincenzo Librandi, Jun 20 2011
(PARI) a(n)=1<<2^n \\ Charles R Greathouse IV, Jul 25 2011
(PARI) a(n)=2^2^n \\ Charles R Greathouse IV, Oct 03 2012
(Haskell)
a001146 = (2 ^) . (2 ^)
a001146_list = iterate (^ 2) 2  Reinhard Zumkeller, Jun 04 2012


CROSSREFS

Cf. A000079, A000215, A026477, A062090, A062091, A112535, A155538.
Cf. A003018, A051179, A173419, A165420.
Sequence in context: A178077 A218148 A112535 * A114641 A152690 A194457
Adjacent sequences: A001143 A001144 A001145 * A001147 A001148 A001149


KEYWORD

nonn,easy,nice,changed


AUTHOR

N. J. A. Sloane


STATUS

approved



