A073669 - OEIS

A073669

a(1) = 1, a(n) = the smallest composite multiple of n such that every partial sum is prime.

1, 4, 6, 8, 10, 12, 42, 24, 72, 20, 132, 36, 52, 14, 30, 16, 68, 54, 76, 80, 126, 88, 92, 24, 100, 26, 108, 112, 116, 30, 310, 128, 66, 204, 70, 36, 74, 76, 78, 120, 902, 84, 430, 44, 360, 460, 188, 240, 294, 100, 204, 104, 106, 54, 110, 280, 342, 116, 708, 60, 244, 62

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OFFSET

1,2

LINKS

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

MAPLE

a[1] := 1:su := 1:for n from 2 to 112 do i := 1: if(isprime(n)) then i := i+1:fi:while(not isprime(i*n+su)) do i := i+1:od:a[n] := i*n:su := su+a[n]:od:seq(a[j], j=1..112);

MATHEMATICA

a[1]=s[1]=1; s[n_] := s[n]=s[n-1]+a[n]; a[n_] := a[n]=For[i=1, True, i++, If[ !PrimeQ[i*n]&&PrimeQ[s[n-1]+i*n], Return[i*n]]]

PROG

(PARI) first(L)=my(v=vector(L), s, k); s=v[1]=1; for(n=2, #v, k=n; while(isprime(k) || !isprime(s+k), k+=n); s+=k; v[n]=k); v \\ Charles R Greathouse IV, Apr 24 2015

CROSSREFS

Sequence in context: A096160 A181055 A225506 * A073670 A090169 A190330

Adjacent sequences: A073666 A073667 A073668 * A073670 A073671 A073672

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Aug 11 2002

EXTENSIONS

Corrected and extended by Sascha Kurz, Jan 30 2003

STATUS

approved