OFFSET
1,1
COMMENTS
The average of twin primes is a member.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
19 is sandwiched between 18 and 20 which are of the form p^2*q where p and q are primes.
MAPLE
k := 0: for j from 2 to 5000 do a := ifactors(j-1): b := ifactors(j+1): if sort([seq(a[2][i][2], i= 1..nops(a[2]))])= sort([seq(b[2][i][2], i= 1..nops(b[2]))]) then k := k+1: c[k] := j: fi: od: seq(c[i], i= 1..k);
MATHEMATICA
f[n_] := Flatten[Table[{ # [[2]]}] & /@ FactorInteger[n]]; Drop[ Select[ Range[415], Sort[f[ # - 1]] == Sort[f[ # + 1]] & ], 1]
PROG
(PARI) isok(n) = vecsort(factor(n-1)[, 2]) == vecsort(factor(n+1)[, 2]); \\ Michel Marcus, Jul 28 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Aug 21 2002
EXTENSIONS
More terms from Sascha Kurz and Robert G. Wilson v, Aug 22 2002
Offset set to 1 by Michel Marcus, Jul 28 2015
STATUS
approved