A280647 Numbers k such that k^3 has an odd number of digits and the middle digit is 7.

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

Lars Blomberg, Table of n, a(n) for n = 1..10000

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

Cf. A280640-A280646, A280648-A280649, A181354.

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

Adjacent sequences: A280644 A280645 A280646 * A280648 A280649 A280650

Keyword

nonn,base,easy

Author

Lars Blomberg, Jan 07 2017

Status

approved