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A137287
a(n) is the number 2 written (prime(n)-1)/2 times followed by the digit 1; a(1)=2.
0
2, 21, 221, 2221, 222221, 2222221, 222222221, 2222222221, 222222222221, 222222222222221, 2222222222222221, 2222222222222222221, 222222222222222222221, 2222222222222222222221, 222222222222222222222221, 222222222222222222222222221, 222222222222222222222222222221
OFFSET
1,1
COMMENTS
Sum of digits of a(n) = prime(n).
FORMULA
A007953(a(n)) = A000040(n). - Michel Marcus, Mar 15 2022
EXAMPLE
prime(7)=17; (17-1)/2=8; a(7) = 222222221, 8*"2" concatenated with "1".
PROG
(PARI) a(n) = if (n==1, 2, fromdigits(concat(vector((prime(n)-1)/2, k, 2), 1))); \\ Michel Marcus, Mar 15 2022
CROSSREFS
Sequence in context: A109684 A292134 A364979 * A155872 A323478 A106412
KEYWORD
easy,nonn,base
AUTHOR
Ctibor O. Zizka, Apr 05 2008
EXTENSIONS
More terms from Michel Marcus, Mar 15 2022
STATUS
approved