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 A158962 a(n) is the smallest number m such that all n numbers m-1, m.m-1, ..., m.m. .. .m-1 are prime, where dot means concatenation. 1
 3, 4, 4, 444, 827868, 10387692, 1885781034 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..7. EXAMPLE All 4 numbers 444-1,444444-1,1+444444444-1,444444444444-1 are prime and 444 is the smallest such number so a(4)=444. MAPLE a:= proc(n) local m; for m do if andmap(isprime, [seq(parse(cat(m\$i))-1, i=1..n)]) then return m fi od end: seq(a(n), n=1..5); # Alois P. Heinz, Apr 14 2021 PROG (Python) from sympy import isprime def A158962(n): m = 1 while True: for i in range(n): if not isprime(int(str(m)*(i+1))-1): break else: return m m += 1 # Chai Wah Wu, Apr 14 2021 CROSSREFS Cf. A153434. Sequence in context: A067137 A060115 A100649 * A263824 A215747 A246667 Adjacent sequences: A158959 A158960 A158961 * A158963 A158964 A158965 KEYWORD base,more,nonn AUTHOR Farideh Firoozbakht, Apr 02 2009 STATUS approved

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Last modified February 22 22:43 EST 2024. Contains 370265 sequences. (Running on oeis4.)