

A051692


a(n) is twice the smallest k such that A051686(k) = prime(n).


2



2, 4, 38, 16, 170, 72, 446, 58, 512, 282, 178, 148, 758, 856, 836, 1592, 1712, 388, 1906, 2606, 2034, 1918, 656, 5924, 1648, 13082, 652, 1514, 2758, 10922, 5758, 18986, 6764, 10570, 20918, 4936, 8188, 5842, 4094, 30710, 15212, 11482, 57932, 14626, 5624, 36232, 16018, 57874
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OFFSET

1,1


COMMENTS

The sequence is based on the first 50000 terms of A051686, in which the first 54 primes (2,3,...,251) appear along with 19 others, the largest of which is A051686(37976) = 823.


LINKS

Table of n, a(n) for n=1..48.


EXAMPLE

The 25th term in this sequence is 1648. This means that prime(25) = 97 arises in A051686 as A051686(1648/2) = A051686(824). Thus, 1648 is the first term in the sequence {..., 2k, ...} = {1648, 1798, 4108, ...} with the property that 2k*97 + 1 = 194k + 1 is also a prime, moreover the smallest one: 159857.


PROG

(PARI) a051686(n) = my(p=2); while(!isprime(2*n*p+1), p = nextprime(p+1)); p;
a(n) = my(k=1); while(a051686(k) != prime(n), k++); 2*k; \\ Michel Marcus, Jun 08 2018


CROSSREFS

Cf. A005384, A051644A051654, A051860, A051861.
Sequence in context: A115250 A018304 A289988 * A053745 A019275 A012433
Adjacent sequences: A051689 A051690 A051691 * A051693 A051694 A051695


KEYWORD

nonn


AUTHOR

Labos Elemer


EXTENSIONS

More terms from Michel Marcus, Jun 08 2018


STATUS

approved



