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 A089948 Smallest prime factor of the concatenation of the first n odd primes. 1
 3, 5, 3, 13, 3, 23, 3, 11, 7, 13, 3, 137, 3, 19, 41, 3, 29, 1087, 7, 23, 3, 641, 7, 79, 124516914725653, 1254907, 983, 691, 19, 9656610616812422838401, 11, 3, 19, 3, 4951, 83404036302541, 3, 372707, 53, 3, 17, 3, 6073, 3, 11, 37, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 3 is the only number < 10000 whose concatenation of odd primes is prime. Conjecture: Beyond 3 the concatenation of odd primes produce only composite numbers. LINKS Table of n, a(n) for n=1..47. MATHEMATICA Join[{x=3}, Table[First[First/@FactorInteger[x=FromDigits[Flatten[IntegerDigits[{x, Prime[n]}]]]]], {n, 3, 30}]] (* Jayanta Basu, Jun 04 2013 *) PROG (PARI) factorconcat(n) = { y=""; forprime(x=3, n, y=concat(Str(y), Str(x)); z=eval(y); a = component(factor(z), 1); print1(a[1]", ") ) } CROSSREFS Cf. A089933. Sequence in context: A049072 A059887 A023585 * A336806 A023583 A266603 Adjacent sequences: A089945 A089946 A089947 * A089949 A089950 A089951 KEYWORD nonn,base AUTHOR Cino Hilliard, Jan 11 2004 EXTENSIONS Edited and extended by Charles R Greathouse IV, Apr 29 2010 STATUS approved

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Last modified May 31 12:47 EDT 2023. Contains 363066 sequences. (Running on oeis4.)