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 A174538 The smallest k such that the number of steps in the n Collatz sequences starting at k+i, i=0..n-1, is always prime. 2
 3, 3, 3, 60, 246, 560, 560, 560, 4722, 4722, 6032, 6666, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 13956, 81488, 81488, 81488, 83840, 89535, 89535, 89535, 282880, 282984, 282984, 282984, 282984 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Indices of A006577 that start a run of at least n primes. We find long sequences of primes, for example there are 55 primes starting at index 282984, namely 83, 101, 127, 251,... LINKS Donovan Johnson, Table of n, a(n) for n = 1..619 (terms <= 10^10) EXAMPLE A006577(3)=7, A006577(4)=2 and A006577(5)=5 are all prime, so a(1)=a(2)=a(3) =3 mark the start of that run. MAPLE A174538 := proc(n)         local k, allp;         for k from 1 do                 allp := true;                 for i from 0 to n-1 do                         if not isprime(A006577(k+i)) then                                 allp := false;                                 break;                         end if;                 end do:                 if allp then                         return k;                 end if;         end do: end proc: # R. J. Mathar, Jul 08 2012 CROSSREFS Cf. A008908, A066906, A070165, A033491. Sequence in context: A025549 A124013 A135584 * A340821 A091323 A174641 Adjacent sequences:  A174535 A174536 A174537 * A174539 A174540 A174541 KEYWORD nonn AUTHOR Michel Lagneau, Mar 21 2010 EXTENSIONS Edited by R. J. Mathar, Jul 08 2012 STATUS approved

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Last modified August 3 19:17 EDT 2021. Contains 346441 sequences. (Running on oeis4.)