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 A249690 Smallest prime k such that sigma(k - m) = sigma(k + m) has exactly n solutions, where m > 0 and sigma is A000203. 0
 2, 19, 131, 179, 1223, 1373, 1931, 4217, 6907, 10861, 9433, 9371, 39877, 63353, 98491, 90749, 83873 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS If k is not required to be a prime the sequence becomes 1, 19, 68, 148, 618, 803, 346, ... . - Derek Orr, Nov 05 2014 LINKS EXAMPLE 19 is in this sequence because sigma(19 - 4) = sigma(19 + 4) = 24 and prime 19 has one solution; 131 is in this sequence because sigma(131 - 20) = sigma(131 + 20) = 152, sigma(131 - 35) = sigma(131 + 35) = 252 and prime 131 has two solutions. PROG (PARI) a(n)=forprime(p=1, , c=0; for(k=1, p-1, if(sigma(p+k)==sigma(p-k), c++)); if(c==n, return(p))) n=0; while(n<10, print1(a(n), ", "); n++) \\ Derek Orr, Nov 04 2014 CROSSREFS Cf. A000203, A070299, A249644. Sequence in context: A055518 A289230 A350568 * A206948 A089364 A178829 Adjacent sequences: A249687 A249688 A249689 * A249691 A249692 A249693 KEYWORD nonn,hard,more AUTHOR Juri-Stepan Gerasimov, Nov 03 2014 EXTENSIONS More terms from Derek Orr, Nov 04 2014 STATUS approved

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Last modified February 3 21:17 EST 2023. Contains 360045 sequences. (Running on oeis4.)