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 A342834 a(n) is the number whose decimal expansion consists of the concatenation of the largest 1-digit prime = 7, the largest 2-digit prime = 97, ... up to the largest n-digit prime = A003618(n). 4
 7, 797, 797997, 7979979973, 797997997399991, 797997997399991999983, 7979979973999919999839999991, 797997997399991999983999999199999989, 797997997399991999983999999199999989999999937, 7979979973999919999839999991999999899999999379999999967 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) has n*(n+1)/2 digits. a(1) = 7 and a(2) = 797, these are only 2 known indices for which a(n) = A338968(n). The decimal expansion of the limit when n -> oo of a(n) is A340220. LINKS EXAMPLE The greatest primes with 1, 2 and 3 digits are respectively 7, 97 and 997, hence, a(3) = 7||97||997 = 797997 where || stands for concatenation. PROG (Python) from sympy import prevprime def aupton(nn): astr, alst = "", [] for n in range(1, nn+1): astr += str(prevprime(10**n)); alst.append(int(astr)) return alst print(aupton(10)) # Michael S. Branicky, Mar 23 2021 (PARI) a(n) = my(s=""); for (k=1, n, s = Str(s, precprime(10^k))); eval(s); \\ Michel Marcus, Mar 24 2021 CROSSREFS Cf. A000217 (number of digits), A338968, A340220, A342835 (number of divisors), A342836 (smallest prime factor). Sequence in context: A001467 A342836 A338968 * A278438 A279120 A047788 Adjacent sequences: A342831 A342832 A342833 * A342835 A342836 A342837 KEYWORD nonn,base AUTHOR Bernard Schott, Mar 23 2021 STATUS approved

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Last modified March 28 23:19 EDT 2023. Contains 361596 sequences. (Running on oeis4.)