A171038 In the sequence of prime numbers, replace all the '7' digits with '4' and vice versa.

2, 3, 5, 4, 11, 13, 14, 19, 23, 29, 31, 34, 71, 73, 74, 53, 59, 61, 64, 41, 43, 49, 83, 89, 94, 101, 103, 104, 109, 113, 124, 131, 134, 139, 179, 151, 154, 163, 164, 143, 149, 181, 191, 193, 194, 199, 211, 223, 224, 229, 233, 239, 271, 251, 254, 263

Offset: 1

Author

N. J. A. Sloane and Vincenzo Librandi, Sep 04 2010

Keywords

• nonn
• base
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Programs

Mathematica

fixp[n_]:=FromDigits[IntegerDigits[n]/.{7->a,4->b}/.{a->4,b->7}]; fixp/@Prime[Range[100]] (* Harvey P. Dale, Apr 25 2011 *)

PARI

a(n)=my(v=[0,1,2,3,7,5,6,4,8,9]);subst(Pol(apply(k->v[k+1], digits(prime(n)))),'x,10) \\ Charles R Greathouse IV, Jul 25 2013