A083060 a(n) is the number of natural numbers k such that A078496(k) = prime(n), where prime(n) denotes the n-th prime.

0, 0, 1, 2, 3, 2, 3, 3, 3, 3, 5, 3, 5, 4, 3, 4, 3, 6, 4, 5, 4, 4, 5, 4, 6, 4, 4, 5, 4, 4, 7, 4, 5, 7, 5, 6, 5, 5, 7, 4, 5, 6, 4, 5, 5, 5, 5, 6, 8, 4, 7, 4, 5, 6, 5, 4, 3, 8, 8, 5, 5, 5, 7, 7, 5, 5, 9, 4, 7, 8, 8, 6, 7, 4, 5, 7, 4, 7, 7, 6, 8, 7, 5, 5, 6, 7, 6

Offset

1,4

Links

Iain Fox, Table of n, a(n) for n = 1..10000

Formula

For n > 2, a(n) = card({k: k > 3; A078496(k) = prime(n)}).

Example

a(3)=1 since there is only k=4 for A078496(k) = prime(3) = 5.
a(8)=3 since there is only k=13,16,18 for A078496(k) = prime(8) = 19.

Prog

(PARI) A078496(n) = {my(p=nextprime(n+1)); while(!isprime(2*n-p), p = nextprime(p+1)); p; }
first(n) = { my(res=vector(n)); for(x=4, prime(n), my(r=primepi(A078496(x))); if(r <= n, res[r]++)); res; } \\ Iain Fox, Nov 23 2017

Crossrefs

Cf. A078496.

Sequence in context: A266119 A026263 A080098 * A346643 A272979 A357610

Adjacent sequences: A083057 A083058 A083059 * A083061 A083062 A083063

Keyword

easy,nonn

Author

Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), Apr 18 2003

Extensions

a(1) and a(2) prepended by Iain Fox, Nov 23 2017

More terms from Iain Fox, Nov 23 2017

Status

approved