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 A078257 a(n) = denominator(N) where N = 0.123...n (concatenation of 1 to n after decimal point). 6
 10, 25, 1000, 5000, 20000, 15625, 10000000, 50000000, 1000000000, 10000000000, 10000000000000, 125000000000000, 100000000000000000, 5000000000000000000, 200000000000000000000, 25000000000000000000000, 10000000000000000000000000, 500000000000000000000000000, 100000000000000000000000000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: sequence is not equal to the sequence of denominators presented in A172495 and A172506. - Jaroslav Krizek, Feb 05 2010 The conjecture is false for both other sequences; see A172495 and A172506 for proofs. - Michael S. Branicky, Nov 30 2022 LINKS Michael S. Branicky, Table of n, a(n) for n = 1..369 FORMULA a(n) = denominator(Sum_{k=1..n} k/10^A058183(k)). - Stefano Spezia, Nov 30 2022 EXAMPLE a(1) = 10 as 10*0.1 = 1, a(2) = 25 as 25*0.12 = 3. PROG (PARI) a(n) = {my(s = ""); for (k=1, n, s = concat(s, Str(k))); denominator(eval(s)/10^(#s)); } \\ Michel Marcus, Jan 15 2019 (Python) from itertools import count, islice def agen(): # generator of terms num, den, pow = 0, 1, 0 for n in count(1): sn = str(n) num = num*10**len(sn) + n den *= 10**len(sn) pow += len(sn) nr, dr, c2, c5 = num, den, pow, pow while nr%2 == 0 and c2 > 0: nr //= 2; dr //= 2; c2 -= 1 while nr%5 == 0 and c5 > 0: nr //= 5; dr //= 5; c5 -= 1 yield dr print(list(islice(agen(), 19))) # Michael S. Branicky, Nov 30 2022 CROSSREFS Cf. A058183, A078258 (numerators), A172495, A172506. Sequence in context: A219377 A156183 A124870 * A059198 A259297 A358774 Adjacent sequences: A078254 A078255 A078256 * A078258 A078259 A078260 KEYWORD base,nonn,frac AUTHOR Amarnath Murthy, Nov 24 2002 EXTENSIONS More terms from Sascha Kurz, Jan 04 2003 More terms from Michel Marcus, Jan 15 2019 STATUS approved

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Last modified March 5 02:31 EST 2024. Contains 370537 sequences. (Running on oeis4.)