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 A241501 Numbers n such that the sum of all numbers formed by deleting two digits from n is equal to n. 1
 167564622641, 174977122641, 175543159858, 175543162247, 183477122641, 183518142444, 191500000000, 2779888721787, 2784986175699, 212148288981849, 212148288982006, 315131893491390, 321400000000000, 417586822240846, 417586822241003, 418112649991390 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Anthony Sand, Table of n, a(n) for n = 1..48 FORMULA For a number with n digits there are nC2 = n!/(n-2)!/2! substrings generated by removing two digits from the original number. So for 12345, these are 345, 245, 235, 234, 145, 135, 134, 125, 124, 123. Sum(x) is defined as the sum of these substrings for a number x and the sequence above is those numbers such that sum(x) = x. EXAMPLE Sum(650000000000000) (15 digits) = 6000000000000 x 13 + 5000000000000 x 13 + 6500000000000 x (78 = 13C2) + 0. PROG (PARI) padbin(n, len) = {b = binary(n); while(length(b) < len, b = concat(0, b); ); b; } isok(n) = {d = digits(n); nb = #d; s = 0; for (j=1, 2^nb-1, if (hammingweight(j) == (nb-2), b = padbin(j, nb); nd = []; k = 1; for (i=1, nb, if (b[i], nd = concat(nd, d[k])); k++; ); s += subst(Pol(nd), x, 10); ); ); s == n; } \\ Michel Marcus, Apr 25 2014 CROSSREFS Cf. A131639 (n equal to sum of all numbers formed by deleting one digit from n). Sequence in context: A271819 A304235 A233503 * A197633 A105295 A288262 Adjacent sequences:  A241498 A241499 A241500 * A241502 A241503 A241504 KEYWORD nonn,base AUTHOR Anthony Sand, Apr 24 2014 STATUS approved

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Last modified October 18 04:57 EDT 2019. Contains 328145 sequences. (Running on oeis4.)