A111677 Array of primes of the type k concatenated with 2n-1 where k < 2n-1. 1---> no prime 13,23 5---> no prime 17,37,47,67 19,29,59,79,89 211,311,811,911 113,313,613,1013,1213 15---> no prime 317,617,... ... Sequence contains the number of terms in the n-th rows.

0, 2, 0, 4, 5, 4, 5, 0, 4, 7, 7, 9, 0, 8, 9, 12, 10, 0, 12, 14, 11, 12, 0, 16, 15, 19, 17, 0, 23, 18, 17, 20, 0, 22, 19, 22, 23, 0, 24, 25, 25, 26, 0, 26, 27, 28, 30, 0, 29, 28, 25, 29, 0, 28, 28, 26, 23, 0, 24, 33, 33, 30, 0, 28, 30, 33, 26, 0, 25, 34, 27, 32, 0, 32, 34, 35, 42, 0, 33

Offset

1,2

Comments

Conjecture: a(n)=0 iff n== 3 (mod 5). [Corrected by R. J. Mathar, Aug 20 2007]

Subsidiary sequences: (1) First occurrence of n in A111677. There are numbers like 3 which probably do not occur in this sequence, let a(3) = -1. (2) Terms that do not occur in A111677.

Links

Table of n, a(n) for n=1..79.

Example

For 2n-1 = 9, we have primes 19,29,59,79 and 89. Hence a(5) = 5.

Maple

cat2 := proc(n, m) n*10^(max(1, ilog10(m)+1))+m ; end: A111677 := proc(nrow) local town1, k, a ; town1 := 2*nrow-1 ; a := [] ; for k from 1 to town1-1 do if isprime(cat2(k, town1)) then a := [op(a), cat2(k, town1)] ; fi ; od; RETURN(nops(a)) ; end: seq(A111677(nrow), nrow=1..80) ; # R. J. Mathar, Aug 20 2007

Crossrefs

Cf. A111676.

Sequence in context: A326052 A004482 A329233 * A326186 A326055 A276331

Adjacent sequences: A111674 A111675 A111676 * A111678 A111679 A111680

Keyword

base,nonn

Author

Amarnath Murthy, Aug 16 2005

Extensions

More terms from R. J. Mathar, Aug 20 2007

Status

approved