A087571 - OEIS

A087571

Smallest prime which has the form of the concatenation n, n-1, n-2, n-3, .., n-k for some k < n, or 0 if no such prime exists.

0, 2, 3, 43, 5, 0, 7, 0, 0, 109, 11, 0, 13, 0, 0, 0, 17, 0, 19, 0, 0, 2221, 23, 2423, 25242322212019181716151413, 0, 2726252423, 0, 29, 0, 31, 0, 0, 3433, 0, 0, 37, 0, 0, 0, 41, 4241, 43, 0, 0, 4645444342414039, 47, 4847464544434241, 0, 0, 5150494847

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OFFSET

1,2

COMMENTS

a(p) = p. Conjecture; There are infinitely many composite numbers n such that a(n) is nonzero.

LINKS

Table of n, a(n) for n=1..51.

EXAMPLE

a(10) = 109 a concatenation of 10 and 9.

a(6) = 0 as no number in the sequence 6,65,654,6543,65432,654321 is prime.

CROSSREFS

Sequence in context: A121475 A334533 A196874 * A126018 A257467 A255092