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A280647
Numbers k such that k^3 has an odd number of digits and the middle digit is 7.
3
31, 32, 105, 111, 128, 130, 149, 167, 173, 191, 192, 475, 483, 484, 491, 509, 524, 530, 534, 545, 546, 550, 556, 559, 584, 590, 592, 597, 614, 619, 624, 628, 637, 641, 665, 668, 692, 701, 725, 743, 750, 760, 781, 793, 809, 824, 836, 837, 843, 852, 861, 864
OFFSET
1,1
COMMENTS
The sequence of cubes starts: 29791, 32768, 1157625, 1367631, 2097152, 2197000, 3307949, 4657463, ...
LINKS
Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.
EXAMPLE
31^3 = 29(7)91, 191^3 = 696(7)871, 619^3 = 2371(7)6659.
MATHEMATICA
Select[Range[865], OddQ[len=Length[IntegerDigits[#^3]]]&&Part[IntegerDigits[#^3], (len+1)/2]==7 &] (* Stefano Spezia, Oct 03 2023 *)
CROSSREFS
See A279420-A279429 for a k^2 version.
See A279430-A279431 for a k^2 version in base 2.
Sequence in context: A042922 A171235 A248815 * A152045 A041479 A194380
KEYWORD
nonn,base,easy
AUTHOR
Lars Blomberg, Jan 07 2017
STATUS
approved