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A116935 Semiprimes (A001358) which are the concatenation of the numbers 1 through n for some n. 2
123, 1234, 1234567, 12345678910111213141516171819202122232425262728293031323334 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

FORMULA

{A007908} intersect {A001358}.

EXAMPLE

a(1) = 123 = 3 * 41.

a(2) = 1234 = 2 * 617.

a(3) = 1234567 = 127 * 9721.

a(4) = 2 * 6172839455055606570758085909601061116212631364146515661667.

CROSSREFS

Cf. A001358, A007908.

Sequence in context: A077379 A135475 * A174173 A103504 A115983 A202132

Adjacent sequences:  A116932 A116933 A116934 * A116936 A116937 A116938

KEYWORD

base,nonn,less

AUTHOR

Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 20 2006

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Last modified February 16 11:21 EST 2012. Contains 205907 sequences.