

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
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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

Table of n, a(n) for n=0..16.


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, p1, if(sigma(p+k)==sigma(pk), 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

JuriStepan Gerasimov, Nov 03 2014


EXTENSIONS

More terms from Derek Orr, Nov 04 2014


STATUS

approved



