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A116935 Semiprimes (A001358) which are the concatenation of the numbers 1 through n for some n. 2

%I #8 Jun 15 2016 10:38:19

%S 123,1234,1234567,

%T 12345678910111213141516171819202122232425262728293031323334

%N Semiprimes (A001358) which are the concatenation of the numbers 1 through n for some n.

%C Next term has 185 digits, and it is thus too large to be included. It is equal to the concatenation of the first 97 integers. - _Giovanni Resta_, Jun 15 2016

%F {A007908} intersect {A001358}.

%e a(1) = 123 = 3 * 41.

%e a(2) = 1234 = 2 * 617.

%e a(3) = 1234567 = 127 * 9721.

%e a(4) = 2 * 6172839455055606570758085909601061116212631364146515661667.

%Y Cf. A001358, A007908.

%K base,nonn,less

%O 1,1

%A _Jonathan Vos Post_, Mar 20 2006

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Last modified June 19 19:59 EDT 2024. Contains 373507 sequences. (Running on oeis4.)