A260989 Integers n such that prime(n-1) + prime(n+1) is a multiple of n.

4, 5, 8, 11, 12, 18, 20, 70, 72, 1053, 4116, 6459, 6460, 40083, 63328, 251742, 399924, 637320, 637322, 637330, 2582288, 2582436, 2582488, 10553828, 16899042, 69709721, 179992913, 179992922, 465769813, 749973302, 749973314, 1208198617, 1208198629

Offset

1,1

Links

Table of n, a(n) for n=1..33.

Zak Seidov, Table of n, (c=prime(n-1)+prime(n-1), c/n

Example

n=4: prime(n-1) + prime(n+1) = 5 + 11 = 16 = 4*n,
n=20: 67 + 73 = 140 = 7*n,
n=16899042: 312632263 + 312632291 = 625264554 = 37*n,
n=69709721: 1394194387 + 1394194453 = 2788388840 = 40*n.

Mathematica

Select[Range[2, 100000], Mod[Prime[# - 1] + Prime[# + 1], #] == 0 &] (* Michael De Vlieger, Aug 07 2015 *)

Prog

(PARI) a=2; b=5; for(n=2, 10^8, c=a+b; if(c%n<1, print1(n", ")); a=nextprime(a+1); b=nextprime(b+1))
(PARI) p=2; q=3; n=1; forprime(r=5, 1e9, if((p+r)%n++==0, print1(n", ")); p=q; q=r) \\ Charles R Greathouse IV, Aug 10 2015
(Magma) [n: n in [2..7*10^3], k in [2..7*10^3] | (NthPrime(n-1) + NthPrime(n+1)) eq n*k]; // Vincenzo Librandi, Aug 07 2015

Crossrefs

Cf. A000040, A004648, A048448, A045924, A023143, A092044, A092045, A156149.

Sequence in context: A190860 A191214 A047376 * A285566 A353044 A293790

Adjacent sequences: A260986 A260987 A260988 * A260990 A260991 A260992

Keyword

nonn

Author

Zak Seidov, Aug 06 2015

Extensions

a(27)-a(33) from Charles R Greathouse IV, Aug 10 2015

Status

approved