The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A016069 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A016069

Numbers k such that k^2 contains exactly 2 distinct digits.
(history; published version)

#49 by Charles R Greathouse IV at Thu Sep 08 08:44:40 EDT 2022

PROG

(MAGMAMagma) [n: n in [0..20000000] | #Set(Intseq(n^2)) eq 2]; // Vincenzo Librandi, Nov 04 2014

Discussion

Thu Sep 08

08:44

OEIS Server: https://oeis.org/edit/global/2944

#48 by Michael De Vlieger at Fri Jul 29 14:13:39 EDT 2022

STATUS

reviewed

approved

#47 by Amiram Eldar at Fri Jul 29 13:38:12 EDT 2022

STATUS

proposed

reviewed

#46 by Bernard Schott at Fri Jul 29 11:54:19 EDT 2022

STATUS

editing

proposed

#45 by Bernard Schott at Fri Jul 29 11:49:20 EDT 2022

COMMENTS

Subsequence of primes is A057659. - Bernard Schott, Jul 29 2022

CROSSREFS

Cf. A016070, A018884, A018885, A057659.

STATUS

approved

editing

Discussion

Fri Jul 29

11:50

Bernard Schott: Comment + crossref.

#44 by N. J. A. Sloane at Fri Dec 17 20:34:25 EST 2021

STATUS

proposed

approved

#43 by Jon E. Schoenfield at Fri Dec 17 19:07:30 EST 2021

STATUS

editing

proposed

#42 by Jon E. Schoenfield at Fri Dec 17 19:06:59 EST 2021

NAME

Numbers n k such that nk^2 contains exactly 2 different distinct digits.

COMMENTS

10^n, k, 2*10^n, k, 3*10^n k for n k > 0 are terms. - Chai Wah Wu, Dec 17 2021

FORMULA

a(n) = ((n-1) mod 3 + 1)*10^(ceilceiling(n/3)-7) for n >= 34 (conjectured). - Chai Wah Wu, Dec 17 2021

EXAMPLE

26 is in the sequence because 26^2 = 676 contains exactly 2 different distinct digits.

STATUS

proposed

editing

#41 by Chai Wah Wu at Fri Dec 17 16:52:36 EST 2021

STATUS

editing

proposed

Discussion

Fri Dec 17

17:13

Wesley Ivan Hurt: Numbers k..

#40 by Chai Wah Wu at Fri Dec 17 16:52:21 EST 2021

COMMENTS

10^n, 2*10^n, 3*10^n for n > 0 are terms. - Chai Wah Wu, Dec 17 2021

FORMULA

a(n) = ((n-1) mod 3 + 1)*10^(ceil(n/3)-7) for n >= 34 (conjectured). - _Chai Wah Wu_, Dec 17 2021