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A129631 Numbers n such that sum of digits of binomial(n+1,n-1) is a prime. 2
2, 6, 15, 20, 24, 31, 34, 43, 52, 61, 67, 70, 76, 85, 88, 91, 94, 97, 103, 106, 112, 115, 121, 124, 127, 130, 133, 136, 139, 141, 145, 151, 154, 160, 163, 166, 169, 178, 181, 190, 193, 196, 199, 200, 208, 211, 217, 226, 229, 232, 235, 238, 241, 247, 250, 259 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

binomial(6+1,6-1)=binomial(7,5)=7!/(5!*2!)=21 --> 2+1=3 prime.

MAPLE

P:=proc(n) local i, k, w; for i from 1 by 1 to n do w:=0; k:=binomial(i+1, i-1); while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if isprime(w) then print(i); fi; od; end: P(1000);

MATHEMATICA

Select[Range[300], PrimeQ[Total[IntegerDigits[Binomial[#+1, #-1]]]]&] (* Harvey P. Dale, Aug 13 2014 *)

CROSSREFS

Sequence in context: A324176 A294942 A227307 * A014847 A013636 A144653

Adjacent sequences:  A129628 A129629 A129630 * A129632 A129633 A129634

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, May 31 2007

STATUS

approved

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Last modified April 9 04:05 EDT 2020. Contains 333343 sequences. (Running on oeis4.)