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 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. 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For each p in row n, (p, 2*A002110(n) - p) is a pair of centered primes at A002110(n) = prime(n)#. The number of terms in row n are 0, 1, 6, 30, 190, ...; this is A147517. LINKS Jean-Marc Rebert, Table of n, a(n) for n = 1..18866 (the first 7 rows). EXAMPLE 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]; ... PROG (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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Last modified February 22 15:05 EST 2020. Contains 332137 sequences. (Running on oeis4.)