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 A173836 Natural numbers n such that the concatenation 1331//n^3 is a prime number. 10
 21, 27, 29, 41, 101, 119, 141, 171, 173, 177, 191, 197, 219, 243, 267, 291, 309, 327, 333, 369, 371, 383, 411, 417, 1019, 1049, 1059, 1091, 1157, 1163, 1211, 1311, 1337, 1343, 1359, 1371, 1379, 1409, 1461, 1473, 1481, 1503, 1521, 1593, 1599, 1613, 1637 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Given the cube n^3 with k = A111393(n) decimal digits, we have to check whether the concatenation, 11^3 * 10^k + n^3, is a prime. The number k of digits that 1331=11^3 is shifted is not a multiple of 3, because the form a^3+b^3 = (a^2+a*b+b^2) * (a - b) cannot construct a prime. REFERENCES K. Haase, P. Mauksch: Spass mit Mathe, Urania-Verlag Leipzig, Verlag Dausien Hanau, 2. Auflage 1985 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE 21 is in the sequence because 21^3=9261, and the concatenation is 13319261=prime(868687). 27 is in the sequence because 27^3=19683, and the concatenation is 133119683=prime(7545064). MATHEMATICA Select[Range[2000], PrimeQ[FromDigits[Join[{1, 3, 3, 1}, IntegerDigits[ #^3]]]]&] (* Harvey P. Dale, Oct 14 2011 *) CROSSREFS Cf. A102006, A167535, A168147, A168219, A168274, A173579, A173733 Sequence in context: A134935 A299594 A318544 * A064507 A249729 A280107 Adjacent sequences:  A173833 A173834 A173835 * A173837 A173838 A173839 KEYWORD base,nonn AUTHOR Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Feb 26 2010 EXTENSIONS Comments sligthly rephrased - R. J. Mathar, Mar 05 2010 STATUS approved

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Last modified March 31 16:44 EDT 2020. Contains 333151 sequences. (Running on oeis4.)