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A100846
Concatenate (1,n,n,1).
7
1001, 1111, 1221, 1331, 1441, 1551, 1661, 1771, 1881, 1991, 110101, 111111, 112121, 113131, 114141, 115151, 116161, 117171, 118181, 119191, 120201, 121211, 122221, 123231, 124241, 125251, 126261, 127271, 128281, 129291, 130301, 131311, 132321
OFFSET
0,1
LINKS
M. F. Hasler, Table of n, a(n) for n = 0..10000 (Terms a(1..9999) from Robert Israel)
FORMULA
G.f.: 1001 + x*(31-11*x)/(1-x)^2 + Sum_{k>=0} 90*(12*10^(2*k)*(1-x)+10^k*x)*x^(10^k)/(1-x)^2. - Robert Israel, Dec 30 2015
EXAMPLE
For n = 0, concatenate(1,n,n,1) is 1001 = a(0).
For n = 5, concatenate(1,n,n,1) is 1551 = a(5).
For n = 10, concatenate(1,n,n,1) is 110101 = a(10).
MAPLE
seq(seq((10^(2*d+1)+1+(10^(d+1)+10)*n), n=`if`(d>1, 10^(d-1), 0) .. 10^d-1), d=1..3);
# Robert Israel, Dec 30 2015, edited for n=0 by M. F. Hasler, Jun 25 2018
MATHEMATICA
For[n = 0, n < 30, n++, l := Floor[Log[10, Min[n, 1]] + 1]; gvout := (n*10^l + n)*10 + 1; m := Floor[Log[10, gvout]]; giveout := 10^(m + 1) + out; Print[giveout]] (* Stefan Steinerberger, Jan 27 2006, edited for n=0 by M. F. Hasler, Jun 25 2018 *)
PROG
(PARI) A100846(n)=eval(Str(1, n, n, 1)) \\ M. F. Hasler, Jun 22 2018
CROSSREFS
Cf. A100896 (3nn3), 7nn7 (A100897), 9nn9 (A102484).
For primes in these sequences: A102496, A102497 (1nn1); A102498, A102499 (3nn3); A102500, A102501 (7nn7); A102502, A102503 (9nn9); A102504 (intersection).
Sequence in context: A317291 A362921 A241946 * A153814 A259080 A100709
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Jan 07 2005
EXTENSIONS
More terms from Stefan Steinerberger, Jan 27 2006
Definition reworded and missing 1001 added by M. F. Hasler, Jun 22 2018
STATUS
approved