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 A178639 Numbers n such that all three values n^2+13^k, k = 1, 2, 3, are prime. 0
 10, 12, 200, 268, 340, 418, 488, 530, 838, 840, 1102, 1720, 1830, 2240, 2410, 2768, 3148, 3202, 3318, 3322, 3958, 4162, 4610, 5080, 5672, 5700, 5722, 5870, 6178, 6302, 6480, 7490, 8130, 8262, 8888, 9132, 9602, 9618, 10638 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A176969. The least-significant digit of all entries is one of 0, 2 or 8, because for odd digits n^2+13^k would be even (not prime), and for digits 4 and 6 the number n^2 + 13^2 is a multiple of 5. REFERENCES B. Bunch: The Kingdom of Infinite Number: A Field Guide, W.H. Freeman, 2001 R. Courant, H. Robbins: What Is Mathematics? An Elementary Approach to Ideas and Methods, Oxford University Press, 1996 G. H. Hardy, E. M. Wright, E. M., An Introduction to the Theory of Numbers (5th edition), Oxford University Press, 1980 LINKS EXAMPLE n=10 is in the sequence because 10^2 + 13 = 113 = prime(30), 10^2 + 13^2 = 269 = prime(57), 10^2 + 13^3 = 2297 = prime(342). n=8888 is in the sequence because 8888^2 + 13 = 78996557 = prime(4614261), 8888^2 + 13^2 = 78996713 = prime(4614269), 8888^2 + 13^3 = 78998741 = prime(4614379). n=6480 defines a prime 6480^2+13^k even for k=0. n=7490 defines a prime 7490^2+13^k even for k=0 and k=4. CROSSREFS Cf. A000040, A000290, A055394, A056899, A086380, A113536, A176371, A176969 Sequence in context: A219213 A078217 A359356 * A087392 A255534 A262422 Adjacent sequences: A178636 A178637 A178638 * A178640 A178641 A178642 KEYWORD nonn AUTHOR Ulrich Krug (leuchtfeuer37(AT)gmx.de), May 31 2010 EXTENSIONS keyword:base removed by R. J. Mathar, Jul 13 2010 STATUS approved

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Last modified February 1 02:31 EST 2023. Contains 359981 sequences. (Running on oeis4.)