A258876 Integers k such that both k and prime(k) have the same digital root.

25, 32, 46, 56, 70, 88, 92, 98, 100, 113, 121, 130, 145, 146, 152, 175, 176, 182, 185, 206, 209, 212, 218, 227, 236, 239, 244, 248, 274, 293, 295, 301, 316, 317, 320, 323, 331, 338, 350, 352, 355, 362, 377, 386, 394, 397, 398, 406, 409, 413, 439

Offset

1,1

Comments

Integers k such that A010888(k) = A038194(k).

Conjecture: a(n) ~ 9n. - Charles R Greathouse IV, Jun 17 2015

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

Both 25 and prime(25) = 97 have 7 for a digital root.
Both 32 and prime(32) = 131 have 5 for a digital root.

Mathematica

Reap[Do[If[FixedPoint[Total[IntegerDigits[#]] &, n] == Mod[Prime[n], 9], Sow[n]], {n, 439}]][[2, 1]] (* Seidov *)
Select[Range[500], Mod[#, 9] == Mod[Prime[#], 9] &] (* Alonso del Arte, Jun 17 2015 *)

Prog

(PARI) isok(n) = (n % 9) == (prime(n) % 9); \\ Michel Marcus, Jun 17 2015
(PARI) n=0; forprime(p=2, 1e4, if((p-n++)%9==0, print1(n", "))) \\ Charles R Greathouse IV, Jun 17 2015

Crossrefs

Cf. A010888, A038194.

Sequence in context: A092100 A172007 A107258 * A263029 A225418 A035140

Adjacent sequences: A258873 A258874 A258875 * A258877 A258878 A258879

Keyword

base,nonn

Author

Zak Seidov, Jun 13 2015

Status

approved