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A157532 a(1) = 2; for n > 1, a(n) = 3. 7
2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) = number of neighboring natural numbers of n (e.g., n, n-1, n+1).

a(n) = A158799(n) for n >= 1. - Jaroslav Krizek, Nov 18 2009

Also decimal expansion of 7/3. - Natan Arie' Consigli, May 02 2015

Decimal expansion of Sum_{i>=0} (4/7)^i. - Bruno Berselli, Aug 23 2017

LINKS

Table of n, a(n) for n=1..95.

FORMULA

a(n) = 1[0]1[1]1...1[n-1]1[n]1, where [0] is zeration or successor (y[0]x = x+1), [1] addition, [2] multiplication, [3] exponentiation, [4] repeated exponentiation, etc. - Natan Arie' Consigli, May 02 2015

G.f.: x*(2+x)/(1-x). - Robert Israel, May 07 2015

EXAMPLE

a(4) = 1[0]1[1]1[2]1[3]1[4]1 = '1+1*1^1^^1 = 3. - Natan Arie' Consigli, May 02 2015

MATHEMATICA

{2}~Join~Table[3, {120}] (* Michael De Vlieger, May 05 2015 *)

PROG

(PARI) A157532(n)=2+(n>1) \\ M. F. Hasler, Jul 30 2015

CROSSREFS

Cf. A254310 (3[0]3[1]...[n]3), A254225 (2[0]2[1]...[n]2).

Except for initial terms, the same as A156752 and A165020. - M. F. Hasler, Jul 30 2015

Sequence in context: A270533 A244919 A158799 * A065684 A065683 A065682

Adjacent sequences:  A157529 A157530 A157531 * A157533 A157534 A157535

KEYWORD

nonn,easy,less,cons

AUTHOR

Jaroslav Krizek, Mar 02 2009

EXTENSIONS

More threes from R. J. Mathar, Mar 14 2009; truncated to three lines by M. F. Hasler, Jul 30 2015

STATUS

approved

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Last modified November 22 00:32 EST 2019. Contains 329383 sequences. (Running on oeis4.)