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A055937 a(n) = a(n-1) * a(n-2) - 1. 4
2, 2, 3, 5, 14, 69, 965, 66584, 64253559, 4278258972455, 274893365303916717344, 1176065006579831683931038116759519, 323292467474902888912311701915651931811127805144397535 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..19

FORMULA

a(n) ~ c^(phi^n), where c = 1.26679081808631741720378389711... and phi = A001622 = (1+sqrt(5))/2 is the golden ratio. - Vaclav Kotesovec, Jun 15 2019

MATHEMATICA

RecurrenceTable[{a[1]==a[2]==2, a[n]==a[n-1]*a[n-2] -1}, a, {n, 15}] (* Vincenzo Librandi, Sep 30 2015 *)

PROG

(Python 2.7.x)

def seq():

    j, k = 2L, 2L

    while k < 2L**3072:

        j, k = k, j * k - 1

        print k

# Joshua D. Olson, Sep 29 2015

(MAGMA) I:=[2, 2]; [n le 2 select I[n] else Self(n-1)*Self(n-2)-1: n in [1..15]]; // Vincenzo Librandi, Sep 30 2015

(PARI) a(n) = if(n<3, 2, a(n-1)*a(n-2)-1);

vector(15, n, a(n)) \\ Altug Alkan, Sep 30 2015

(Sage)

def a(n):

    if (n==1 or n==2): return 2

    else: return a(n-1)*a(n-2) -1

[a(n) for n in (1..15)] # G. C. Greubel, Jun 07 2019

CROSSREFS

A152446 uses largest prime < a(n-1)*a(n-2) instead of subtracting 1. - Joshua D. Olson, Sep 29 2015

Cf. A007660, A121258.

Sequence in context: A065994 A152446 A265789 * A090255 A228162 A080669

Adjacent sequences:  A055934 A055935 A055936 * A055938 A055939 A055940

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jul 05 2000

STATUS

approved

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Last modified February 22 18:03 EST 2020. Contains 332148 sequences. (Running on oeis4.)