A260405 Irregular array read by rows, where the n-th row lists the primes p < A002110(n) such that 2*A002110(n) - p is also prime.
5, 7, 13, 17, 19, 23, 29, 11, 19, 23, 31, 37, 41, 47, 53, 61, 67, 71, 73, 83, 89, 103, 107, 109, 113, 127, 137, 139, 149, 151, 157, 163, 179, 181, 191, 193, 197, 17, 23, 29, 37, 53, 59, 71, 73, 97, 101, 103, 107, 113, 127, 137, 139, 157, 163, 173, 179, 197, 199, 211, 223, 229, 257, 263, 271
Offset: 1
Examples
The first row is empty. T(2,1) = 5 because (5,7) is a pair of primes centered at A002110(2) = prime(2)# = 6. Triangle starts: []; [5]; [7, 13, 17, 19, 23, 29]; [11, 19, 23, 31, 37, 41, 47, 53, 61, 67, 71, 73, 83, 89, 103, 107, 109, 113, 127, 137, 139, 149, 151, 157, 163, 179, 181, 191, 193, 197]; ...
Links
- Jean-Marc Rebert, Table of n, a(n) for n = 1..18866 (the first 7 rows).
Programs
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PARI
a147517=[0,1,6,30,190,1564,17075,226758,3792532] a002110(n)=prod(i=1, n, prime(i)) a(n)=my(k=2,maxk=2,primorielle=2,s=0,y=5);if(n==1, y=5, maxk=2;while(sum(k=2, k=maxk, a147517[k])
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PARI
row(n) = {v = []; pn = prod(i=1, n, prime(i)); forprime(p=1, pn-1, if (isprime(2*pn-p), v = concat(v, p))); v;} \\ Michel Marcus, Aug 02 2015 -
PARI
a002110(n) = prod(p=1,n,prime(i)); T(n,k) = my(P= a002110(n),compteur = 0,q=0,y=-1);forprime(p=1,P-1,q = 2*P-p;if(isprime(q),compteur++;if(compteur== k,y=p;y;break)));y
Comments