OFFSET
1,1
COMMENTS
If k = 10*R_m + 2, with m >= 1, then the concatenation of k with 8*k equals (30*R_m + 6)^2, so A047855 \ {1,2} is a subsequence. - Bernard Schott, Apr 09 2022
Numbers k such that A009470(k) is a square. - Michel Marcus, Apr 09 2022
The numbers 28, 278, 2778, ..., 2*10^k + 7*(10^k - 1)/9 + 1, ..., k >= 1, are terms, because the concatenation forms the squares 28224 = 168^2, 2782224 = 1668^2, 277822224 = 16668^2, ..., (10^m + 2*(10^m - 1)/3 + 2)^2, m >= 2, ... - Marius A. Burtea, Apr 10 2022
LINKS
Marius A. Burtea, Table of n, a(n) for n = 1..176
EXAMPLE
3_24 = 18^2.
11112_88896 = 33336^2.
PROG
(PARI) isok(k) = issquare(eval(Str(k, 8*k))); \\ Michel Marcus, Apr 09 2022
(Magma) [n:n in [1..20000000]|IsSquare(Seqint(Intseq(8*n) cat Intseq(n)))]; // Marius A. Burtea, Apr 10 2022
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Jan 25 2006
EXTENSIONS
More terms from Marius A. Burtea, Apr 13 2022
STATUS
approved