OFFSET
1,1
COMMENTS
Conjecture: a(1) is the only prime number.
No other prime terms up to a(8000). - Giovanni Resta, May 07 2016
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
EXAMPLE
a(1) = concatenate("1", "1") = 11.
a(2) = concatenate("2", "1", "1", "2") = 2112.
a(3) = concatenate("3", "2", "1", "1", "2", "3") = 321123.
MATHEMATICA
FromDigits@Flatten@IntegerDigits@Join[Reverse@#, #] & /@ Table[Range@n, {n, 20}]
PROG
(PARI) a(n)={fromdigits(concat(concat(Vecrev(vector(n, i, digits(i)))), concat(vector(n, i, digits(i)))))} \\ Andrew Howroyd, Dec 23 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
José de Jesús Camacho Medina, May 03 2016
EXTENSIONS
Terms a(11) and beyond from Andrew Howroyd, Dec 23 2019
STATUS
approved