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A081494 Start with Pascal's triangle; form a triangle by sliding down n steps from top on both sides and including the horizontal row, deleting the inner numbers; a(n) = sum of entries on perimeter of triangle. 4
1, 3, 7, 13, 23, 41, 75, 141, 271, 529, 1043, 2069, 4119, 8217, 16411, 32797, 65567, 131105, 262179, 524325, 1048615, 2097193, 4194347, 8388653, 16777263, 33554481, 67108915, 134217781, 268435511, 536870969, 1073741883, 2147483709 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..32.

FORMULA

For n > 1, a(n) = A061761(n-1). - David Wasserman, Jun 03 2004

EXAMPLE

The triangle pertaining to n = 4 is obtained from the solid triangle

        1

      1   1

    1   2   1

  1   3   3   1

giving

        1

      1   1

    1       1

  1   3   3   1

and the sum of all the numbers is 13, so a(4) = 13.

MAPLE

restart:a:= proc(n) option remember; if n=0 then 1 else add((binomial (n, j)+2), j=0..n-1) fi end: seq (a(n), n=0..31); # Zerinvary Lajos, Mar 29 2009

CROSSREFS

Cf. A081495, A081496, A081497.

Sequence in context: A066624 A317783 A061761 * A161909 A281131 A173168

Adjacent sequences:  A081491 A081492 A081493 * A081495 A081496 A081497

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Mar 25 2003

EXTENSIONS

Corrected and extended by David Wasserman, Jun 03 2004

STATUS

approved

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Last modified November 14 01:24 EST 2019. Contains 329108 sequences. (Running on oeis4.)