A179975 Smallest k such that k*10^n is a sum of two successive primes.

5, 3, 1, 6, 6, 6, 14, 6, 9, 19, 21, 21, 42, 93, 21, 6, 11, 2, 12, 111, 37, 39, 63, 38, 42, 24, 15, 15, 60, 6, 39, 82, 47, 58, 337, 49, 72, 25, 34, 21, 6, 107, 128, 96, 20, 2, 63, 231, 70, 7, 62, 144, 28, 151, 157, 33, 98, 55, 134, 162, 87, 201, 124, 303, 64, 106, 130, 13, 43

Offset

0,1

Comments

From Robert G. Wilson v, Aug 11 2010: (Start)

A179975 n's such that a(n)=1: 3, 335, ..., .

A179975 First occurrence of k: 3, 18, 2, ???, 1, 4, 50, 162, 9, 335, 17, 19, 68, 7, 27, ..., .

Records: 5, 6, 14, 19, 21, 42, 93, 111, 337, 449, 862, 1049, 1062, 1122, 1280, 2278, 3168, 4290, ..., . (End)

Links

Robert G. Wilson v, Table of n, a(n) for n = 0..400.

Dario Alejandro Alpern, Brilliant numbers

Example

a(0)=5 because 5=2+3
a(1)=3 because 30=13+17
a(2)=1 because 100=47+53
a(3)=6 because 6000=2999+3001.

Mathematica

Join[{5, 3}, Reap[Do[Do[n=10^m k; If[n==PreviousPrime[n/2]+NextPrime[n/2], Sow[k]; Break[]], {k, 2000}], {m, 2, 50}]][[2, 1]]]
f[n_] := Block[{k = 1, tn = 10^n}, While[h = k*tn/2; NextPrime[h, -1] + NextPrime@h != k*tn, k++ ]; k]; f[1] = 3; Array[f, 70, 0] (* Robert G. Wilson v, Aug 11 2010 *)

Crossrefs

Cf. A064397, A071220, A074924, A074925.

Cf. A033873, A033874, A005235, A055211, A038804, A084475.

Sequence in context: A111487 A011505 A373672 * A019926 A249538 A322932

Adjacent sequences: A179972 A179973 A179974 * A179976 A179977 A179978

Keyword

nonn

Author

Zak Seidov, Aug 04 2010

Extensions

More terms from Robert G. Wilson v, Aug 11 2010

Status

approved