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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
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
OFFSET
1,2
COMMENTS
a(p) = p. Conjecture; There are infinitely many composite numbers n such that a(n) is nonzero.
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
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Sep 16 2003
EXTENSIONS
Corrected and extended by Gabriel Cunningham (gcasey(AT)mit.edu), Sep 21 2003
STATUS
approved