A388987 Square array A(n,k) = A326127(A388981(n, k)), read by descending antidiagonals.

13, 19, 28, 17, 46, 66, 21, 34, 92, 134, 29, 46, 86, 210, 276, 73, 52, 96, 148, 326, 404, 41, 316, 116, 176, 320, 528, 630, 33, 78, 1866, 190, 342, 430, 704, 818, 41, 64, 188, 7190, 386, 482, 698, 990, 1220, 121, 70, 126, 274, 35124, 560, 800, 932, 1538, 1770, 45, 562, 146, 218, 494, 71384, 834, 970, 1266, 1892, 2140

Offset

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..22155; the first 210 antidiagonals

Index entries for sequences related to prime indices in the factorization of n.

Index entries for sequences related to sigma(n).

Example

The top left corner of the array:
k=  |    1     2     3     4     5        6     7     8     9       10    11
----+------------------------------------------------------------------------
1   |   13,   19,   17,   21,   29,      73,   41,   33,   41,     121,   45,
2   |   28,   46,   34,   46,   52,     316,   78,   64,   70,     562,   82,
3   |   66,   92,   86,   96,  116,    1866,  188,  126,  146,    2762,  176,
4   |  134,  210,  148,  176,  190,    7190,  274,  218,  260,   11690,  274,
5   |  276,  326,  320,  342,  386,   35124,  494,  452,  474,   42962,  540,
6   |  404,  528,  430,  482,  560,   71384,  628,  586,  664,   95714,  716,
7   |  630,  704,  698,  800,  834,  187902,  944,  936, 1004,  215210, 1038,
8   |  818,  990,  932,  970, 1084,  304058, 1422, 1160, 1198,  375290, 1274,
9   | 1220, 1538, 1266, 1404, 1496,  661412, 1706, 1542, 1634,  846650, 1772,
10  | 1770, 1892, 1944, 2060, 2118, 1515570, 2480, 2234, 2408, 1645322, 2582,

Prog

(PARI)
up_to_cols = 210;
A326127(n) = (sigma(n)-core(n)-n);
A388984list(up_to) = { my(v=vector(up_to), i=0); forstep(n=2, oo, 2, if(isprime(core(n)) && !isprimepower(n), i++; v[i] = n; if(i==up_to, return(v)))); };
v388984 = A388984list(up_to_cols);
A388984(n) = v388984[n];
up_to = binomial(up_to_cols+1, 2)
A388981sq(row, col) = if(1==row, A388984(col), my(f = factor(A388984(col))); for(i=1, #f~, f[i, 1] = prime(primepi(f[i, 1])+(row-1))); factorback(f));
A388987sq(row, col) = A326127(A388981sq(row, col));
A388987list(up_to) = { my(v = vector(up_to), i=0); for(a=1, oo, for(col=1, a, i++; if(i > up_to, return(v)); v[i] = A388987sq(col, (a-(col-1))))); (v); };
v388987 = A388987list(up_to);
A388987(n) = v388987[n];

Crossrefs

Cf. A000203, A007913, A326127, A388981.

Cf. also A388988.

Sequence in context: A227092 A123840 A258589 * A103804 A063640 A092104

Adjacent sequences: A388984 A388985 A388986 * A388988 A388989 A388990

Keyword

nonn,tabl

Author

Antti Karttunen, Sep 22 2025

Status

approved