The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A127542 Number of subsets of {1,2,3,...,n} whose sum is prime. 6
 0, 2, 4, 7, 12, 22, 42, 76, 139, 267, 516, 999, 1951, 3824, 7486, 14681, 28797, 56191, 108921, 210746, 410016, 804971, 1591352, 3153835, 6249154, 12380967, 24553237, 48731373, 96622022, 191012244, 376293782, 739671592, 1454332766, 2867413428 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS T. D. Noe and Charles R Greathouse IV, Table of n, a(n) for n = 1..1000 (first 100 terms from Noe) EXAMPLE The subsets of {1,2,3} that sum to a prime are {1,2}, {2}, {3}, {2,3}. Thus a(3)=4. MAPLE with(combinat): a:=proc(n) local ct, pn, j:ct:=0: pn:=powerset(n): for j from 1 to 2^n do if isprime(add(pn[j][i], i=1..nops(pn[j]))) =true then ct:=ct+1 else ct:=ct fi: od: end: seq(a(n), n=1..18); MATHEMATICA g[n_] := Block[{p = Product[1 + z^i, {i, n}]}, Sum[Boole[PrimeQ[k]]*Coefficient[p, z, k], {k, 0, n*(n + 1)/2}]]; Array[g, 34] (* Ray Chandler, Mar 05 2007 *) PROG (Haskell) import Data.List (subsequences) a127542 = length . filter ((== 1) . a010051 . sum) .                           subsequences . enumFromTo 1 -- Reinhard Zumkeller, Feb 22 2012, Oct 27 2010 (PARI) a(n)=my(v=Vec(prod(i=1, n, x^i+1)), s); forprime(p=2, #v, s+=v[p]); s \\ Charles R Greathouse IV, Dec 19 2014 (PARI) first(n)=my(v=vector(n), P=1, s); for(k=1, n, P*=1+'x^n; s=0; forprime(p=2, k*(k+1)/2, s+=polcoeff(P, p)); v[k]=s); v \\ Charles R Greathouse IV, Dec 19 2014 CROSSREFS Cf. A053632, A126024, A181522, A010051. Row sums of A282516. Sequence in context: A268306 A018179 A190165 * A023432 A072641 A280352 Adjacent sequences:  A127539 A127540 A127541 * A127543 A127544 A127545 KEYWORD nonn AUTHOR Emeric Deutsch, Mar 03 2007 EXTENSIONS Extended by Ray Chandler, Mar 05 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 29 14:13 EDT 2020. Contains 337431 sequences. (Running on oeis4.)