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A083060
a(n) is the number of natural numbers k such that A078496(k) = prime(n), where prime(n) denotes the n-th prime.
2
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
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
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