A134534 Numbers n such that the sum of the digits of 11^n is prime.

1, 9, 10, 11, 13, 15, 19, 21, 22, 25, 31, 32, 51, 52, 57, 58, 59, 62, 63, 68, 69, 70, 75, 76, 80, 81, 84, 91, 93, 95, 98, 99, 100, 101, 103, 107, 109, 114, 117, 124, 131, 132, 133, 135, 137, 139, 142, 153, 158, 159, 161, 164, 175, 176, 182, 190, 192, 194, 198, 207

Offset: 1

Author

Paolo P. Lava and Giorgio Balzarotti, Oct 30 2007

Keywords

• easy
• nonn
• base

Examples

			11^9=2357947691 and 2+3+5+7+9+4+7+6+9+1=53 is prime.
		

Links

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

Crossrefs

Cf. A076203, A134532, A134533, A134535.

Programs

Maple

P:=proc(n)local cont,i,k,w; if isprime(n) then cont:=0; while cont<1000 do cont:=cont+1; w:=0; k:=n^cont; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if isprime(w) then print(cont); fi; od; fi; end: P(11);

Mathematica

Select[Range[250],PrimeQ[Total[IntegerDigits[11^#]]]&] (* Harvey P. Dale, Sep 29 2012 *)