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 A121325 Juxtaposition of the prime factors of 4*n^2 + 1 with multiplicity. 0
 5, 17, 37, 5, 13, 101, 5, 29, 197, 257, 5, 5, 13, 401, 5, 97, 577, 677, 5, 157, 17, 53, 5, 5, 41, 13, 89, 1297, 5, 17, 17, 1601, 5, 353, 13, 149, 29, 73, 5, 461, 41, 61, 5, 541, 2917, 3137, 5, 673, 13, 277, 5, 769, 17, 241, 4357, 5, 5, 5, 37, 13, 13, 29, 5, 17, 61, 5477, 53 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS These numbers are all of the form 4m+1. LINKS Table of n, a(n) for n=1..67. EXAMPLE For n=4, 4n^2+1 = 65 = 5*13. 5 and 13 are the 4th and 5th entries. MATHEMATICA Flatten[Table[Table[First[#], {Last[#]}]&/@FactorInteger[4*n^2+1], {n, 60}]] (* Harvey P. Dale, Dec 19 2011 *) PROG (PARI) fourxsqp1 (n)= { forstep(x=1, n, 1, y=4*x^2+1; a=ifactor(y); for(j=1, length(a), print1(a[j]", ") ) ) } ifactor(n) = \The vector of the integer factors of n with multiplicity. { local(f, j, k, flist); flist=[]; f=Vec(factor(n)); for(j=1, length(f[1]), for(k = 1, f[2][j], flist = concat(flist, f[1][j]) ); ); return(flist) } CROSSREFS Sequence in context: A186029 A083048 A123669 * A256970 A145689 A321658 Adjacent sequences: A121322 A121323 A121324 * A121326 A121327 A121328 KEYWORD nonn AUTHOR Cino Hilliard, Aug 26 2006 STATUS approved

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Last modified July 21 18:01 EDT 2024. Contains 374475 sequences. (Running on oeis4.)