This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A225100 First occurrence of n in A225099, or -1 if n does not appear in A225099. 1
 0, 12, 36, 370, 3770, 12410, 202130, 197210, 81770, 9151610, 16046810, 12625730, 21899930, 95336930, 9549410, 416392730, 1016275130, 338609570, 789396530, 601741010, 254885930, 10083683090, 4690939370, 29207671610, 30431277890, 22264417370, 23231920010, 10838858810, 37462976330 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Least integer k representable as a sum of two distinct nontrivial prime powers (A025475 except the first term) in exactly n ways. LINKS MATHEMATICA nn = 300000; p = Sort[Flatten[Table[Prime[n]^i, {n, PrimePi[Sqrt[nn]]}, {i, 2, Log[Prime[n], nn]}]]]; t =Sort[Select[Flatten[Table[p[[i]] + p[[j]], {i, Length[p] - 1}, {j, i + 1, Length[p]}]], # <= nn &]]; t2 = Table[Count[t, n], {n, 0, nn}]; n2 = Max[t2]; Table[Position[t2, n, 1, 1][[1, 1]], {n, 0, n2}] - 1(* T. D. Noe, Apr 29 2013 *) PROG (C) #include #include #define TOP (5ULL<<16) typedef unsigned long long U64; U64 *mem, pwFlat[TOP], primes[TOP]={2}, f[96]; int pp_compare(const void *p1, const void *p2) {   if (*(U64*)p1 == *(U64*)p2) return 0;   if (*(U64*)p1 < *(U64*)p2) return -1;   return 1; } int main() {   U64 i, j, k, p, pp=1, pfp;   mem = (U64*)malloc(3ULL<<30);   for (i = 3; i < TOP; i+=2) {     for (p = 0; p < pp; ++p)  if (i%primes[p] == 0) break;     if (p==pp)  primes[pp++] = i;   }   for (pfp = i = 0; i < pp; ++i)     for (j = primes[i]*primes[i]; j < TOP*TOP; j *= primes[i])       pwFlat[pfp++] = j;   for (k = i = 0; i < pfp; ++i)     for (j = i+1; j < pfp; ++j)       if ((p = pwFlat[i] + pwFlat[j]) < TOP*TOP) mem[k++] = p;   qsort(mem, k, 8, pp_compare);   p = mem[0];   for (i = j = mem[k] = 1; i <= k; ++i) {     if (p == mem[i])  { ++j; continue; }     if (j < 96 && f[j] == 0)  f[j] = p;     p = mem[i];     j = 1;   }   for (i = 0; i < 96; ++i)  printf("%llu, ", f[i]);   return 0; } CROSSREFS Cf. A225099. Sequence in context: A278583 A216381 A085331 * A058040 A130164 A144973 Adjacent sequences:  A225097 A225098 A225099 * A225101 A225102 A225103 KEYWORD nonn AUTHOR Alex Ratushnyak, Apr 27 2013 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 May 22 21:17 EDT 2019. Contains 323504 sequences. (Running on oeis4.)