cp's OEIS Frontend

A171617 a(n)=k is the smallest exponent of N=2^k of first prime(1)=2 where at least 5 equal decimal digits "n n n n n" appear in the decimal representation of N (n=0,1,...9).

%I A171617 #13 Oct 16 2012 17:50:00
%S A171617 1491,485,314,221,315,973,220,317,316,422
%N A171617 a(n)=k is the smallest exponent of N=2^k of first prime(1)=2 where at least 5 equal decimal digits "n n n n n" appear in the decimal representation of N (n=0,1,...9).
%C A171617 If we change the definition to allow for not just the digits but for the numbers, say "10" then this sequence can be extended. a(10) would become 263528 and a(11) would equal 165742. - _Robert G. Wilson v_, Oct 13 2012
%D A171617 E. J. Burr, American Mathematical Monthly (December 1963, 70(10), pp. 1101-2
%D A171617 Julian Havil, Impossible?: Surprising Solutions to Counterintuitive Conundrums, Princeton University Press 2008
%D A171617 Ross Honsberger, Ingenuity in mathematics, Random House/Singer School Division 1970
%e A171617 0: 2^1491: 449 decimal digits, "00000" appears on decimals 397 - 401.
%e A171617 1: 2^485: 146 decimal digits, "11111" appears on decimals 22 - 26.
%e A171617 2: 2^314: 95 decimal digits, "22222" appears on decimals 64 - 68.
%e A171617 3: 2^221: 67 decimal digits, "33333" appears on decimals 7 - 11.
%e A171617 4: 2^315: 95 decimal digits, "44444" appears on decimals 64 - 68.
%e A171617 5: 2^973: 293 decimal digits, "555555" (6 "5's") appears on decimals 230 - 25.
%e A171617 6: 2^220: 67 decimal digits, "66666" appears on decimals 7 - 11.
%e A171617 7: 2^317: 96 decimal digits, "77777" appears on decimals 65 - 69.
%e A171617 8: 2^316: 96 decimal digits, "88888" appears on decimals 65 - 69.
%e A171617 9: 2^422: 128 decimal digits, "99999" appears on decimals 83 - 87.
%t A171617 f[n_] := Block[{k = 1, m = IntegerString[n]}, mm = m <> m <> m <> m <> m; While[ StringPosition[ ToString[2^k], mm] == {}, k++]; k]; Array[f, 10, 0] (* _Robert G. Wilson v_, Oct 13 2012 *)
%Y A171617 Cf. A000079, A018802, A171132, A171242, A171489.
%K A171617 nonn,base,fini,full
%O A171617 0,1
%A A171617 Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Dec 13 2009