A063552 Smallest k such that 2^k has exactly n 7's in its decimal representation.

1, 15, 27, 24, 46, 75, 116, 152, 157, 170, 181, 237, 297, 282, 360, 214, 317, 380, 475, 311, 417, 440, 424, 538, 535, 427, 474, 632, 654, 651, 810, 766, 832, 626, 848, 824, 780, 931, 897, 992, 889, 1004, 981, 1079, 1087, 1123, 1224, 1186, 892, 1174, 1200

Offset

0,2

Links

Harry J. Smith, Table of n, a(n) for n = 0..150

Mathematica

a = {}; Do[k = 1; While[ Count[ IntegerDigits[2^k], 7] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
Join[{1}, With[{c=DigitCount[#, 10, 7]&/@(2^Range[0, 1300])}, Flatten[ Table[ Position[c, n, 1, 1], {n, 60}]]]-1] (* Harvey P. Dale, Oct 14 2012 *)

Prog

(PARI) a(n)={my(k=1); while(n<>#select(d->d==7, digits(2^k)), k++); k} \\ Harry J. Smith, Aug 26 2009, Andrew Howroyd, Jun 26 2018

Crossrefs

Cf. A063115, A063426, A063429, A063430, A063526, A063540, A063553, A063554.

Sequence in context: A240914 A205881 A132452 * A131541 A359205 A080945

Adjacent sequences: A063549 A063550 A063551 * A063553 A063554 A063555

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 10 2001

Extensions

Name corrected by Jon E. Schoenfield, Jun 25 2018

Status

approved