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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 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.)