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A249690
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Smallest prime k such that sigma(k - m) = sigma(k + m) has exactly n solutions, where m > 0 and sigma is A000203.
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0
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2, 19, 131, 179, 1223, 1373, 1931, 4217, 6907, 10861, 9433, 9371, 39877, 63353, 98491, 90749, 83873
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OFFSET
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0,1
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COMMENTS
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If k is not required to be a prime the sequence becomes 1, 19, 68, 148, 618, 803, 346, ... . - Derek Orr, Nov 05 2014
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LINKS
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Table of n, a(n) for n=0..16.
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EXAMPLE
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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.
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PROG
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(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
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CROSSREFS
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Cf. A000203, A070299, A249644.
Sequence in context: A055518 A289230 A350568 * A206948 A089364 A178829
Adjacent sequences: A249687 A249688 A249689 * A249691 A249692 A249693
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KEYWORD
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nonn,hard,more
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AUTHOR
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Juri-Stepan Gerasimov, Nov 03 2014
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EXTENSIONS
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More terms from Derek Orr, Nov 04 2014
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STATUS
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approved
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