A249690 Smallest prime k such that sigma(k - m) = sigma(k + m) has exactly n solutions, where m > 0 and sigma is A000203.

2, 19, 131, 179, 1223, 1373, 1931, 4217, 6907, 10861, 9433, 9371, 39877, 63353, 98491, 90749, 83873

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, 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 * A082862 A206948 A089364

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