A280646 -id:A280646 - cp's OEIS frontend

A280645 Numbers k such that k^3 has an odd number of digits and the middle digit is 5.

26, 43, 107, 109, 119, 122, 136, 139, 144, 150, 177, 179, 197, 203, 205, 472, 476, 494, 499, 501, 506, 510, 523, 537, 555, 561, 563, 568, 583, 603, 608, 629, 636, 649, 664, 694, 696, 726, 752, 753, 762, 766, 769, 780, 795, 796, 807, 814, 819, 826, 831, 845

Offset: 1

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 17576, 79507, 1225043, 1295029, 1685159, 1815848, 2515456, 2685619, ...

			26^3 = 17(5)76, 150^3 = 337(5)000, 603^3 = 2192(5)6227

Lars Blomberg, Table of n, a(n) for n = 1..10000
Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.

Cf. A280640-A280644, A280646-A280649, A181354.
See A279420-A279429 for a k^2 version.
See A279430-A279431 for a k^2 version in base 2.

Select[Range[900],OddQ[IntegerLength[#^3]]&&IntegerDigits[#^3][[(IntegerLength[ #^3]+1)/2]]==5&] (* Harvey P. Dale, Aug 24 2017 *)

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

Original entry on oeis.org

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

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 29791, 32768, 1157625, 1367631, 2097152, 2197000, 3307949, 4657463, ...

			31^3 = 29(7)91, 191^3 = 696(7)871, 619^3 = 2371(7)6659.

Lars Blomberg, Table of n, a(n) for n = 1..10000
Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.

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.

Select[Range[865], OddQ[len=Length[IntegerDigits[#^3]]]&&Part[IntegerDigits[#^3], (len+1)/2]==7 &] (* Stefano Spezia, Oct 03 2023 *)

cp's OEIS Frontend

A280645 Numbers k such that k^3 has an odd number of digits and the middle digit is 5.

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