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 A343145 a(n) is the least positive number k such that applying x->prime(x) n times results in a number that ends in k. 1
 1, 7, 6447, 7, 1, 1, 69, 9, 1, 1, 1, 7, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS EXAMPLE a(1) = 7 since prime(7) = 17 which ends in 7. a(2) = 6447 since prime(prime(6447)) = 806447 which ends in 6447. a(3) = 7 since prime(prime(prime(7)))=277 which ends in 7. a(4) = 1 since prime(prime(prime(prime(1)))) = 11 which ends in 1. a(5) = 1 since prime(prime(prime(prime(prime(1))))) = 31 which ends in 1. a(6) = 69 since prime(prime(prime(prime(prime(prime(69)))))) = 54615469 which ends in 69. a(7) = 9 since prime(prime(prime(prime(prime(prime(prime(9))))))) = 4535189 which ends in 9. PROG (Python) def A343145(n):     k = 1     while True:         m = k         for _ in range(n):             m = prime(m)         if m % 10**(len(str(k))) == k:             return k         k += 1         while not (k % 2 and k % 5):             k += 1 (PARI) primemap(n, tms) = my(x=n); for(i=1, tms, x=prime(x)); x enddigits(n, len) = ((n/10^len - floor(n/10^len)) * 10^len) a(n) = for(k=1, oo, my(x=k); if(enddigits(primemap(k, n), #Str(k))==k, return(k))) \\ Felix FrÃ¶hlich, Apr 14 2021 CROSSREFS Cf. A046883, A074978, A343128. Sequence in context: A246853 A225067 A281358 * A068575 A158400 A221628 Adjacent sequences:  A343142 A343143 A343144 * A343146 A343147 A343148 KEYWORD nonn,hard,base,more AUTHOR Chai Wah Wu, Apr 06 2021 STATUS approved

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Last modified September 21 15:47 EDT 2021. Contains 347598 sequences. (Running on oeis4.)