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A134532 Numbers n such that the sum of the digits of 5^n is prime. 4
1, 2, 4, 5, 6, 7, 13, 19, 20, 22, 26, 27, 29, 33, 34, 36, 41, 43, 44, 50, 54, 55, 58, 59, 60, 66, 69, 70, 74, 75, 81, 85, 91, 95, 97, 99, 100, 101, 110, 112, 125, 127, 129, 131, 133, 134, 136, 142, 143, 145, 146, 148, 153, 156, 157, 163, 165, 178, 187, 189, 190, 196 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

EXAMPLE

5^2=25 and 2+5=7 is prime.

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(5);

MATHEMATICA

a={}; For[n=1, n<200, n++, If[PrimeQ[Plus@@IntegerDigits[5^n]], AppendTo[a, n]]]; a (* Vincenzo Librandi, Apr 17 2013 *)

CROSSREFS

Cf. A076203, A134533, A134534, A134535.

Sequence in context: A317185 A276005 A092058 * A282278 A268448 A230581

Adjacent sequences:  A134529 A134530 A134531 * A134533 A134534 A134535

KEYWORD

easy,nonn,base

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Oct 30 2007

STATUS

approved

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Last modified February 19 18:22 EST 2019. Contains 320327 sequences. (Running on oeis4.)