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A066956 a(n) is the number of ways of placing '+' and '-' among the digits 123456789 so that the result of the expression is n, '-' before 1 not allowed. 3
11, 26, 11, 18, 8, 21, 12, 17, 8, 22, 12, 21, 11, 16, 15, 20, 8, 17, 11, 20, 15, 16, 11, 23, 18, 13, 14, 21, 15, 19, 17, 14, 19, 19, 7, 14, 19, 19, 17, 18, 16, 17, 18, 10, 15, 26, 18, 15, 16, 12, 17, 19, 9, 17, 21, 16, 13, 14, 16, 17, 17, 11, 13, 22, 14, 13, 15, 15, 15, 17, 7 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) = 0 for all but finitely many n. In particular, a(n) = 0 for n > 123456789. - Charles R Greathouse IV, Aug 20 2012

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..34668

EXAMPLE

a(4) = 8 because 4 = 12-34-56-7+89 = 12-3-4-5-6-7+8+9 = 12-3+45-67+8+9 = 12-3+4-5+6+7-8-9 = 12-3+4+5-6-7+8-9 = 12+3-4-5+6-7+8-9 = 12+3-4+5-6-7-8+9 = 1+2-34+5+6+7+8+9 and only for these.

PROG

(Python)

from collections import Counter

from itertools import product, zip_longest

def aupton(nn):

    digs = list("123456789")

    c = Counter(eval("".join(filter(None, sum(zip_longest(digs, ops), ())))) for ops in product(["-", "+", ""], repeat=8))

    return [c[k] for k in range(nn+1)]

print(aupton(70)) # Michael S. Branicky, Nov 26 2021

CROSSREFS

Cf. A066957.

Sequence in context: A043940 A220434 A191720 * A250611 A137015 A260903

Adjacent sequences:  A066953 A066954 A066955 * A066957 A066958 A066959

KEYWORD

nice,nonn,base

AUTHOR

Miklos SZABO (mike(AT)ludens.elte.hu), Feb 01 2002

STATUS

approved

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Last modified October 6 03:14 EDT 2022. Contains 357261 sequences. (Running on oeis4.)