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A048543 a(n) is the smallest value of m such that A002378(m), the m-th oblong number, contains exactly n 7's. 11
8, 108, 878, 870, 8813, 27924, 84129, 882483, 2788865, 7601169, 88190572, 421518419, 4204014483, 26034169427, 42305694389, 88022598108, 546605779129 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..17.

Eric Weisstein's World of Mathematics, Pronic Number

EXAMPLE

From Jesse Sealand, Oct 05 2019: (Start)

a(1) = 8 since A002378(8) = 72;

a(2) = 108 since A002378(36) = 11772;

a(3) = 878 since A002378(182) = 771762;

a(4) = 870 since A002378(1817) = 757770, etc.

(End).

PROG

(Python)

def A048543(n):

    k, m = 1, 2

    while True:

        if str(m).count('7') == n:

            return k

        k += 1

        m += 2*k # Chai Wah Wu, Mar 23 2018

CROSSREFS

Cf. A048544, A002378.

Cf. A048529, A048531, A048533, A048535, A048537, A048539, A048541, A048545, A048547.

Sequence in context: A276296 A164749 A264487 * A300468 A326101 A300807

Adjacent sequences:  A048540 A048541 A048542 * A048544 A048545 A048546

KEYWORD

nonn,base,more

AUTHOR

Patrick De Geest, May 15 1999

EXTENSIONS

a(13)-a(16) from Lars Blomberg, Jun 10 2011

Name edited by Jesse Sealand, Oct 05 2019

a(17) from Giovanni Resta, Oct 09 2019

STATUS

approved

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Last modified August 13 18:03 EDT 2022. Contains 356107 sequences. (Running on oeis4.)